Technical Bad Idle, Judder and Brake revving

Currently reading:
Technical Bad Idle, Judder and Brake revving

Lots going on there..

Revs rising as you Brake.. a few options

Big feet..
Easy to check

The cross.car rod rubbing something
Does braking change the TPS values?

Vacuum issue..
Only time I have encountered this was on a Diesel.. so no engine running effect ( they use a vac pump..)

Can you plug the vac line at the TB??


OBVIOUSLY NO SERVO at that point
 
It's the throttle postion sensor that is on the throttle body as there is no pedal position sensor on this model.

If you think, both A and B circuits on a FBW car would be linked. Input from A at the pedal should match A at the throttle.
Same goes for B.
Not on the Panda the signals from each go directly to the ECU
If there is a problem on either circuit it could be at either end, pedal or throttle end it would still think there is an issue with the throttle position.
With the right software you should be able to drag the extended DTC out of the ECU which would perhaps point to which isn't right.
There would be 4 values, 2 at the pedal and 2 at the throttle so in most cases it should be able to spot the one that's incorrect.

But there's no pedel sensors on this model only the throttle position sensors
Correct but the ECU has seen an error in this pedal circuit. Glitch wiring who knows
so using a car with FBW is like comparing apples with oranges.
The link between pedal and throttle is linked via cable, so there is only 2 position sensors on the throttle body linked to the ECU.
Now what has happened is the ECU has seen there's a problem with the throttle position, A as under or over reading or doesn't match B.
There's no other sensors involved, just the two differing readings from the two sensors on the throttle body.
Correct but we have no error code for the throttle body
I understand the value of the absolute throttle position is small, but these sensors alter a signal voltage of 5v and return the results back the the ECU as low as 0.1v, so I would expect some change in manifold pressure even if the throttle opening is so small,
There no or very little raise in revs. Surely the manifold pressure will stay the same.
it would change the pressure in there and show some small change, but there isn't any.
Plus if there's no input on the throttle, where is this throttle position signal coming from?

I think the OP still changed the throttle body to solve a throttle position sensor fault which caused some running issues.
As this has failed to solve it, it's not impossible but it's likely it's not the throttle body, throttle position sensors or the pedal position sensors (which is doesn't have) which is why I said look at the wiring.
We have no errors for a throttle position sensor, the OP has fitted an OEM brand new throttle body made no change. This is as I would expect.


If you disconnects a sensor and break the close loop cycle the engine revs drop back to normal.
 
Ok so I had a chance to look at the car today and covered lots of tests. I did not learn a lot, as my understanding is poor, so still need help with this. All tests are run on a warm engine with the airbox off (like in the first picture - but with the vacuum line fully connected).

Summary:
  • Loads of testing has been undertaken
  • Brake booster seems ok but there appears to be a vacuum leak somewhere on that line. However, even when this is isolated the car idles high
  • I have not found unusual spikes in any of the telemetry data though the idle control valve seems to be behaving differently
  • Swapping lambda sensors did not help and I could not find an air leak near the throttle body or inlet manifold
  • Car is driving notably well but idle remains high (1,500 to 2,000 RPM when engine hot)

Thanks for all the help but please only read beyond this if you are a glutton for punishment!!!!

These are the detailed steps I took:
1) Check Air Leak on Vacuum Line to Brake Booster:

• I ran the engine and pumped the brake, the engine rev’ed/stalled. Then I disconnected the vacuum line to the brake booster at the inlet manifold and blocked the port. Pumping the brake did not rev/stall the engine. Note in all subsequent tests the vacuum line has been reconnected
Block_Vacuum_Port.jpg

• Then I checked the brake booster and it passed all steps and seemed really good to me. The test is here: Test
• I checked the behaviour more carefully and I did notice that when the brake is pushed in the engine rpm changes slightly for a moment, when it is held depressed there is no change in engine rpm and when it is released it revs / increased RPM more significantly but again momentarily. So the changes in RPM only occur momentarily when the brake is moved and not when it is held. This made me wonder is this normal behaviour – as cycling the brake is not typical?
• Even when the vacuum line was disconnected and the port blocked the engine was still idling high. Due to this I did not look further at the booster side as I felt there was still a problem somewhere else.
Questions:
Q1.1:
Is cycling the brake (say every second or twice a second) leading to engine reving actually normal behaviour?
Q1.2: As the engine idles high when the vacuum line is removed, and the port to the inlet manifold blocked, am I right in assuming that there is an idle issue somewhere else anyway?

2) Check Vacuum Leak – Inlet Manifold and Breather Pipe:
• I really tried to find something but struggled to get anything. I sprayed "easy start" all over the places of interest and nothing. Later I tried WD40 with a long spray nozzle and sprayed it vertically down the manifold interface with the cylinders using the four bolts as a spatial reference. Could not find sign of a leak, e.g., spray affecting engine tone
• I removed the breather pipe (see below). I blocked two ends with my fingers and blew in the remaining end until I was close to passing out. Nothing, no leaks evident.
Breather.jpg

Questions:
Q2.1:
Anywhere else I should look for a leak? I will try the evap circuit when I can, I have not gotten to it yet.

3) Check Throttle Pedal and Position Sensor on throttle body:
• I had a good look at the throttle pedal and, as you probably all know, there is no electrical connection or sensors, just a physical throttle cable that runs through the bulkhead to the engine bay and over to the throttle body. The white plastic "hex cog" part pulls the cable
• I removed the fault code to see how long before it reappears!
Throttle_Pedal.jpg


4) Swap O2 Sensors:
• So I found a new lambda sensor in the garage and fitted it in the pre-cat position. I then ran the engine and then put the old pre-cat sensor in the post-cat place and ran it again. The high idle was still present in all of these tests. The two used sensor are shown below.
Removed lambda_Sensors.jpg


5) Logged and Review Some Longer Run Sensor Data:
• I was looking for spikes or anomalies, which are hard to find for my acquisition rate and did not find anything in: Coolant temperature data or throttle position data (see below for TPS data for an engine off test, but similar for engine on). Also kept an eye on others and found nothing that stood out to me.
Data_Testing_Throttle_Position_Sensor.jpg


6) Some General Checks:
• I ran the engine and monitored the data. I noticed that I could not hear a click from the idle control valve as I had before so I looked at the data. The expected behaviour is not evident, i.e., click from throttle body followed by revs dropping and inlet pressure increasing! I show this below where on top I have a prior measurement (I expected this again) but below is the most recent one (I got this one) - I do not see the idle control valve impact and could not hear it click?
Idle_Control_Valve_Test_Comparison.jpg

• I was told that the middle two spark plugs were connected to the same coil pack I had a look and this is correct! Interesting. In looking at this I noticed that the harnessing for this coil pack was damaged so I wrapped insulating tape around it just in case. This harness sits over the engine and the outer black protection was embrittled and flaking off. The wires looked ok.
Before Image:
Coil_Pack_Harness_Damage.jpg

After picture:
Coil_Pack_Harness_Fix.jpg

• I have been driving the car since the latest changes and it is driving smoothly and I have not been able to provoke any judder yet. Maybe it will appear but I would have expected it to have occurred a number of times over the distance I drove. However idle remains high
• I have not checked the evap circuit as I need to find out more about this before I take it on

P.S. if you have read this far you have truly earned my respect!
 
It might be different on cable throttles as the manifolds are different

But if you take the airbox off and leave all the breather tubes disconnected on my car the car still idles normally

The system is designed to compensate as it’s all still seen by the MAP sensor. The only place after the sensor you have tested with easy start

I guess you can double check if there is a massive leak by putting your hand over here picture below and seeing if the car still idles high

The missing flaky insulation is only there to protect the wires inside from chafing.

Great you have protected them again but this will not effect.

Coolant temperature sensor another one checked of the list

we also know it’s not an O2 sensor one that’s checked of the list

we also know it’s not the brake servo yet one that’s checked of the list
Doesn’t seem like progress but so far we have eliminated quite a bit without spending on parts.


On your scan tool what’s the voltage with the engine tuning. No idea why but it’s one of the checks Fiat recommend for high idle

We have to work out whether the ECU is receiving the wrong information or it not sending it to the idle control valve.
F2BE92BF-25BA-4008-BFC9-2F1A88142A42.png
 
So you are still having idle issues.
We all now know there is no pedal sensor, you have physically checked.
You have swapped the throttle body for a new one.
You are still getting the same code and running issues with the new body as with the old.

As I have already mentioned, P0120 is a throttle position sensor code.

This version of software your car runs just doesn't comprehend what a pedal positon sensor is.
Later versions will, but not this model so you need to stop thinking of this as similar problems that a car with pedal sensors might suffer and interpret the code as such.

It is comparing circuit A with circuit B of the throttle position sensors on the throttle body.
It seeing an under, over or mismatched signal.

If there is a short in one of the circuits it thinks the throttle is wide open,
or
If there is a break in the circuit it thinks the throttle is closed.

You might be tempted to think it's a short and WOT problem due to the high rpm at idle, but either can cause the ECU to run in a failsafe mode.
This will cause a "keep me running and get me home" program loop which will have a naturally high rpm and overly rich fueling as that is far safer to the engine than a lean fueling mix as it no longer trusts the signals it's getting from the TPS's.
 
So you are still having idle issues.
We all now know there is no pedal sensor, you have physically checked.
You have swapped the throttle body for a new one.
You are still getting the same code and running issues with the new body as with the old.

As I have already mentioned, P0120 is a throttle position sensor code.

This version of software your car runs just doesn't comprehend what a pedal positon sensor is.
Later versions will, but not this model so you need to stop thinking of this as similar problems that a car with pedal sensors might suffer and interpret the code as such.

It is comparing circuit A with circuit B of the throttle position sensors on the throttle body.
It seeing an under, over or mismatched signal.

If there is a short in one of the circuits it thinks the throttle is wide open,
or
If there is a break in the circuit it thinks the throttle is closed.

You might be tempted to think it's a short and WOT problem due to the high rpm at idle, but either can cause the ECU to run in a failsafe mode.
This will cause a "keep me running and get me home" program loop which will have a naturally high rpm and overly rich fueling as that is far safer to the engine than a lean fueling mix as it no longer trusts the signals it's getting from the TPS's.


We have at least two were blowing compressed air in the pedal has fixed P0120 errors

We have at least two where reseating the pedal connector has fixed the problem including my own that have fixed a P0120 error

We have one where changing the pedal has fixed the problem. I believe someone else changed a pedal for one out of a diesel and the P0120 didn’t return

The OP has a logged P0120 error but no pedal potentiometer. Wiring might still be present ?

The throttle pedal sensor is connected directly to the ECU and is no way connected electrically to the throttle body. It is connect to the A/C which I see the OP has


I was waiting to see if the error returned. Which it hasn’t yet It’s might just be a glitch.

I would like to move on from the TPS error for now an concentrate on the high revs



the information on the web is hit and miss leading I have already said there are mistakes, I know, I have wasted time in the past looking at the wrong part. I would believe the fault codes as per fiats own examiner software over anything else which I have already posted.

Several people have changed the throttle body on fiats for this code and it hasn’t fixed the problem. I wouldn’t expect it to.



EE1A45A1-1801-4E01-9C7C-3BE49852EA99.jpeg
 
The fault code is returning, see point 3 on the OP's last post. They keep resetting it.
"I removed the fault code to see how long before it reappears!"

It isn't much use comparing a car with a different management system that the OP's.
Back when their car was made there was no pedal sensor, no wiring for a pedal sensor and nothing for the ECU to compare against for a pedal sensor fault. The software the car runs is different to later models.


Looking back through some of the posted data, the rpm does look rather stable if high. It seems to settle into this 1600+ idle and hold it without it bouncing around.

Looking at the 02 sensor log on the other page, that looks it's running just a little rich, (0.2 and 0.8 of a volt) but again it's fairly stable. (after the manifold pressure settles down after the brake pump)

Neither of these suggest it has an air leak, if it did I would expect the rpms to bounce around while the O2 went lean and the fuel trim maxed out trying to add fuel, but it's not really doing this.

I suspect it's in some form of safe running mode.
I have seen something similar before with an older Panda we had. (2007 model)
It turned out to be a O2 heater sensor issue (no codes though) It wouldn't trip into Closed Loop after a cold start (only a hot start), it just went into a Failsafe Open Loop setting. (not a normal Open Loop setting).
In this Failsafe Open Loop setting it increased RPM and enrichened the mix slightly.

I suspect we have something similar, the ECU is having a problem with something and it's going into a Failsafe mode which includes increasing the RPM and enrichening the mixture slightly.

Then we come back to this P0120.
The software is interpreting whatever fault there is as this code and we are getting conflicting evidence of what is means.
Cars with pedal sensors can throw this up and it can be a pedal sensor issue.
Cars without pedal sensors car throw this up and it's a throttle position sensor issue.

There is only one pair of potentiometers on the system and they are on the throttle body and if we take the logical step for a non pedal sensor car, where does that leave us, at the throttle body.

So now we can't find an air leak and don't see real evidence of one.
The O2's have been swapped.
The MAP unplugged (seems to work)
And the throttle body has been swapped but we have the same issue.

Seems the parts might be ok, so now where?
The wiring is probably next to check.

As it's a pretty cheap and easy test, I would be probing the 5v feed to the throttle body plug to check that.
Then trying to identify the A and B circuit at the throttle body plug and ECU plug and bridging them with a test wire, A first, then B and then both.(remembering to reset the DTC before firing it up)
 
This is interesting.

We know FBW cars have a pair on potentiometers at the pedal and a pair on the throttle body.

Where is the DTC in the list for faults with the throttle body potentiomters?
There doesn't appear to be any.

I suspect they are monitored on the same circuit as the pedal ones, so without the pedal ones, what does P0120 relate to?
 
This is interesting.

We know FBW cars have a pair on potentiometers at the pedal and a pair on the throttle body.

Where is the DTC in the list for faults with the throttle body potentiomters?
There doesn't appear to be any.

I suspect they are monitored on the same circuit as the pedal ones, so without the pedal ones, what does P0120 relate to?
Codes around P2112 throttle body
Codes around P0120 throttle pedal

Codes aren’t 100% because a mismatch in expected numbers can confuse the ECU

Unlikely on a Panda as on there FBW throttles body’s and pedals both have two POTs

But here we circuit error so doesn’t apply.
 
There so much more we can be checking

Such as is the ECU actually talking to the idle control valve. An actuator test would be a good move for this

Expect revs vs actual and so on
 
P2112 is the throttle motor actuator not the throttle position sensor.

With a electronic throttle control, the throttle sensor and pedal sensor is the same circuit which is why P0120 can be the pedal or the throttle body.

The lastest Ford, Toyota, GM, Renault, Citroen, VW, Nissan all refer to P0120 as the Throttle/Pedal Position Sensor Circuit A malfunction and if you dig down into their diagnostic tests for this code, they test for both signals from pedal and throttle body as they are all part of the same circuit.

If you look through some of their older diagnostic stuff, P0120 is only referred to as Throttle Position Sensor Circuit A malfunction.

There is also some interesting information on the Failsafe systems on some disgnostic sites.
An electronic throttle control system would cut the throttle control but increase the throttle opening by around 6° in failsafe mode to keep the car moving (slowly).

As this is not a electronic throttle control system it can't control the main throttle to increase rpm by it's self in fail safe, so it utilises the IVC to increase the rpm but the driver still has control over the main throttle as it's physically linked.

There's no pedal sensors but there is a problem on the throttle position circuit, the only thing there is the throttle position sensors, the wiring to it and the ECU.
 
P2112 is the throttle motor actuator not the throttle position sensor.
I didn’t say P2112 I said around which is still correct. None of which helps the original poster. The code has been cleared once. I will wait to see if its reoccurring.
With a electronic throttle control, the throttle sensor and pedal sensor is the same circuit which is why P0120 can be the pedal or the throttle body.

The lastest Ford, Toyota, GM, Renault, Citroen, VW, Nissan all refer to P0120 as the Throttle/Pedal Position Sensor Circuit A malfunction and if you dig down into their diagnostic tests for this code, they test for both signals from pedal and throttle body as they are all part of the same circuit.

If you look through some of their older diagnostic stuff, P0120 is only referred to as Throttle Position Sensor Circuit A malfunction.

There is also some interesting information on the Failsafe systems on some disgnostic sites.
An electronic throttle control system would cut the throttle control but increase the throttle opening by around 6° in failsafe mode to keep the car moving (slowly).

As this is not a electronic throttle control system it can't control the main throttle to increase rpm by it's self in fail safe, so it utilises the IVC to increase the rpm but the driver still has control over the main throttle as it's physically linked.

There's no pedal sensors but there is a problem on the throttle position circuit, the only thing there is the throttle position sensors, the wiring to it and the ECU.
It’s not a Ford, Toyota, GM, Renault, Citroen, VW, Nissan

Here’s a fiat issued document





DD8D0185-5FA5-429F-815C-E215446905AC.jpeg
 
I obviously presumed too much.
I thought it was common knowledge that P0*** codes were generic diagnostic codes that are shared by all OBD2 compliant vehicles no matter who made them.
Trouble codes work like this.
P is powertrain
C is chassis
B is body
U is network

The next character
0 is generic
1 is manufacturer specific
2 and 3 are other manufacturer specific

The third character
1 is fuel and air metering
2 is fuel and air metering injection management
3 is ignition
4 is emissions
5 is vehicle speed control
6 is computer output
7 & 8 transmission

The final two characters are the specific fault index characters.


And again, we need to look back to what that specific code relates to back in 2009 with a vehicle with a certain fuel management system and not get confused with what it could possible relate to with a newer vehicle with a different fuel management system.
Because there is this cross over, most describe this code as Throttle and/or Pedal sensor circuit A malfunction, but if we look back at generic DTC lists before ETCS were common, it's just the throttle position sensor as there is no other on that system.

Is there an adjustment screw on the throttle body? Can you adjust idle speed when the engine is hot?

To me, it looks like the ECU has control over the idle speed via the ICV.
There's no other way air can enter the engine with a closed throttle butterfly on this model unless there is a post throttle body air leak or via the ICV.
If it was the case of an air leak, we would certainly see other evidence of it but the logs posted seem to show something different. The O2 and idle speed look too controlled.

If that's the case the high idle isn't the actual problem, it's a temporary remedy created by the ECU to another problem with the fuel management system.
It's an " I can't trust something so am I going to flag a DTC and take control of what I can't trust to get you home".
What has it taken control of and therefore can't trust, the air entering the engine.

So there's something going on that is causing the ECU to take control of the air entering the engine and that is where to look.
With or without the code, the clue is what the ECU has taken control of.

The OP looks like they have grasped that as they have replaced the throttle body, but it hasn't fixed the issue unless both throttle bodies are duff.
That's possible, but there's more to the control circuit of the air than the actual part, like the wiring or the ECU.

There is a possibility something else is wrong and that maybe the code isn't correct, I am not writting that off.
But by ignoring the code, anything else is like looking for a needle in a haystack at the moment.

Start with following the obvious clues first, they have already started the process, follow it through to the end to confirm it either way, otherwise you may never find the fault.
 
I obviously presumed too much.
I thought it was common knowledge that P0*** codes were generic diagnostic codes that are shared by all OBD2 compliant vehicles no matter who made them.
Trouble codes work like this.
P is powertrain
C is chassis
B is body
U is network

The next character
0 is generic
1 is manufacturer specific
2 and 3 are other manufacturer specific

The third character
1 is fuel and air metering
2 is fuel and air metering injection management
3 is ignition
4 is emissions
5 is vehicle speed control
6 is computer output
7 & 8 transmission

The final two characters are the specific fault index characters.
Correct the code is a generic pedal or throttle. It’s up to the manufacture to chose how to use it. This is why look up on the internet doesn’t always work. You need to look at manufactures specific or better still model specific codes
And again, we need to look back to what that specific code relates to back in 2009 with a vehicle with a certain fuel management system and not get confused with what it could possible relate to with a newer vehicle with a different fuel management system.
Because there is this cross over, most describe this code as Throttle and/or Pedal sensor circuit A malfunction, but if we look back at generic DTC lists before ETCS were common, it's just the throttle position sensor as there is no other on that system.
Same as above it’s up the the manufacture how to use this code
To me, it looks like the ECU has control over the idle speed via the ICV.
Correct
There's no other way air can enter the engine with a closed throttle butterfly on this model unless there is a post throttle body air leak or via the ICV.
If it was the case of an air leak, we would certainly see other evidence of it but the logs posted seem to show something different. The O2 and idle speed look too controlled.
Correct
If that's the case the high idle isn't the actual problem, it's a temporary remedy created by the ECU to another problem with the fuel management system.
It's an " I can't trust something so am I going to flag a DTC and take control of what I can't trust to get you home".
What has it taken control of and therefore can't trust, the air entering the engine.
Correct but there are other causes. The ECU command the revs to go high with the compressor among other things. Delphi software and others allows you to look at the Revs the ECU is demanding and allow you to test the ICV. As of yet we don’t even know if the ICV is moving.
So there's something going on that is causing the ECU to take control of the air entering the engine and that is where to look.
Correct assuming the ECU is working, the ICV is working, the cabling between to two is work and the ECU isn’t getting a signal from the compressor or cooling fans to raise the revs
With or without the code, the clue is what the ECU has taken control of.
Correct. A bigger clue would be if the same code came back it’s been cleared once. It not unusual for codes to appear while doing work on the car but aren’t genuine CANBUS errors being the most common
The OP looks like they have grasped that as they have replaced the throttle body, but it hasn't fixed the issue unless both throttle bodies are duff.
Correct. Changing a ICV would have been cheaper. As it turned out wouldn’t help
That's possible, but there's more to the control circuit of the air than the actual part, like the wiring or the ECU.
Correct. We don’t even know yet if the ICV is even operating
There is a possibility something else is wrong and that maybe the code isn't correct, I am not writting that off.
But by ignoring the code, anything else is like looking for a needle in a haystack at the moment.
That why I keep say we should see if the code reappears. Both the compressor and coolant fan share some of the same pins on the ECU
Start with following the obvious clues first, they have already started the process, follow it through to the end to confirm it either way, otherwise you may never find the fault.
Correct
 
There's another clue in the rpm it is choosing.
It's not choosing a similar rpm to when the AC compressor kicks in or a cold start rpm. (see below)
It's reving high enough to get you off the road without any other throttle input.

It would be interesting to see what the status of the fuel system is at start up and as it warms up.
Is it going from open to a normal closed loop or is it detecting the fault and going into a "safe open loop" setting as it warms up.
That would at least put them on the track it's a purposely set rpm.

The data isn't all there but on post 25, on the last graph, the rpm seems to step up.
It that is coming out of cold start open loop and tripping into a high rpm safe fuelling setting?

The codes are generic, the manufacturers do not choose what these mean, they mean the same for all.
As onboard management systems have changed, they have fitted in with these codes which is why we have had this discussion regarding pedal or throttle sensor.
The original, pre ETCS meant is was just the throttle body sensors as there is nothing at the other end, but since they have added pedal sensors the code of a circuit fault in that system is the same, but it could be at either end.

I made the presumption that before every attempt to fix the problem the OP would have reset the fault code, otherwise they've been wasting their time.
In fact they mentioned resetting the code and as there's only one code mentioned in the entire thread, I thought that a safe presumption.
 
Back
Top