Technical engine started idling really high!!

[matty23]

Hi,

All of a sudden my Panda 1.2 8v has started idling as though the engine is cold. I already know the engine revs to around 1,200 rpm when cold but the engine is doing this when hot and fluctuating between 1,200rpm and 1,500rpm.

First thing I thought of was the cable for the throttle was sticking and so I put my foot under the pedal expecting the pedal to lift higher due to it sticking. But that wasn't the case.

This evening I took it upon myself to remove the airbox to have a good look at the throttle body/airbox/pipes for damage or cracks. The throttle body was clean and the rubber, engine breather pipe was still in good shape.

Nothing appears out of place and there are no engine lights and even after plugging my diagnostic machine into it, no codes were found!! Everything seems fine, but all of a sudden the engine revs to 1,200rpm and will no go lower than that! However, I've noticed the needle for the rev counter doesn't stick at 1,200, it fluctuates between 1,200 and 1,300 rpm or even jumping as high as 1,500rpm.

Please help.

Matt.

 

[irc]

Does you diagnostic machine show the throttle opening percentage?
If it does, does the percentage fluctuate when you are not touching the pedal?

If not, try the following:
Turn off engine.
Press throttle pedal right down, slowly, 3 or 4 times.
Press down 1 more time and release quickly.
Restart engine and see if it is still misbehaving.
If it is OK then I suspect it is the throttle sensor (or possibly grot in the throttle body, even though it looks clean)
If not, try cleaning the ECU connectors with proper contact cleaner (there are posts on the forum with really good info on how to do this)
irc

 

[Goudrons]

I had a similar problem with our old Active.

It would start normally, with the usual high idle, but once warm it continued to idle fast and waver between 1200 - 1500 rpm.

Once hot, if it was turned off and on again it would be ok until the next cold start, then it would do it all over again

No error codes were stored.

I ended up logging a few cold starts with a cheap bluetooth OBD tool and Torque Pro App and I noticed the fueling was failing to drop out of it's normal Open Loop warm up setting and wasn't tripping into Closed Loop as it should have done.

I just kept getting a "Fuel Status - System Fault" report and the car was sticking in some sort of Open Loop safety setting.

The coolant temp was responding ok, so the ECU was getting the signal to change fueling and the upstream O2 was responding reasonable well (for an extra rich mix due to the Open Loop it was still stuck in)

The only thing left I could think of was the O2 preheater.
I pulled both O2's and check both + & - feeds for both and they appeared ok.

I decided if the upstream had a dodgy preheater it wouldn't matter in the downstream position, so swapped them over and bingo, the fault went away.
Clean starts, warmed up and tripped into a normal "Closed Loop" fuel status with a normal warm idle.

So it might be worth a try, if your diagnostic tool allows you, to cold start and watch the fuel system status, it should go from Open Loop to Closed Loop within a few minutes.

 

[murfman53]

Hi Goudrons,

I was interested to see that by switching your 02 sensors you cured your problems. Good lad!!!
Correct me if I'm wrong, but don't the 2 02 sensors operate on different input information.
The precat 02 (sometimes refered as an AIR/FUEL sensor AF) monitors the air/fuel ratio, as where the post cat 02 sensor monitors the amount of oxygen that passes thru it.
I wasn't aware they they could be changed into different positions, but obviously you managed to cure your problems.
As a matter of interest, does your scan tool give fuel trims info on short term and long term?
I had a similar problem recently on an 2005 panda 1.2 02 post cat sensor remaining in open loop, and like you, I checked the sensor, and all seemed fine. I decided to replace it with a new one, and bingo all was well and running like a Rolls Royce.
Thanks for your post Goudrons, interesting solution, must remember this one in future.
John.

 

[matty23]

Thank-you so much for your help,

My diagnostic machine is more of just a code reader and can delete fault codes. Unfortunately it's not a more technically advanced one.

I did decide to remove the throttle position sensor & idle control valve from the throttle body whilst also disconnecting the battery for around 10 minutes.

Got back into the car and allowed the engine to warm up with the lights, air con, heated window activated and the revs fluctuated around 900rpm. I revved the engine up to 3,000rpm but it jumped back down to 900rpm if that makes sense. The engine, when the throttle was released did not release the revs quickly, it was as though it had to come down in stages; 3,000 down to 1,500, down to 1,200 then 900 - it only held at each stage for less than a second, but it was still noticeable.

Matt.

 

[murfman53]

Thank-you so much for your help,

My diagnostic machine is more of just a code reader and can delete fault codes. Unfortunately it's not a more technically advanced one.

I did decide to remove the throttle position sensor & idle control valve from the throttle body whilst also disconnecting the battery for around 10 minutes.

Got back into the car and allowed the engine to warm up with the lights, air con, heated window activated and the revs fluctuated around 900rpm. I revved the engine up to 3,000rpm but it jumped back down to 900rpm if that makes sense. The engine, when the throttle was released did not release the revs quickly, it was as though it had to come down in stages; 3,000 down to 1,500, down to 1,200 then 900 - it only held at each stage for less than a second, but it was still noticeable.


Matt.

Why not try your test again, but turn off your lights,air con, and heated rear window. The heated rear window uses a lot of juice, believe or not, and all these accessories turned on puts extra load on your battery. This might account for your "jump downs" in rpm. Just a thought. Assuming its a petrol model, your idle rpm should run around 750rpm.

John.

 

[Goudrons]

The both pre and post cat O2's self generate an electrical signal based on exhaust temp.

They are the only sensors that do this, they'll self produce up to 0.9v. (more with a blowtorch!)
All other sensors alter a feed voltage (5v) somehow and return that altered voltage back to the ECU.

The hotter the temp, the leaner the engine (more air) the higher the voltage it produces.

The upstream or precat sensor controls the how much fuel is injected in "Closed Loop", so once the engine starts to warm it soon trips from "Open Loop" (a preset fueling status to warm up).

The ECU will add fuel to richen the mix when the voltage signal is high, then amazingly, this cools the exhaust gases, so the ECU takes away fuel and on and on.
This pre cat sensor should do this once every second or so, what's known as "Switching", up and down, 0.1 to around 0.9v.
A good average or mid switch "trim" voltage would be on or very near 0.45v for near perfect fueling.

This trip from Open to Closed Loop now happens a lot sooner that it used to as each sensor has a pre heating element these days. No longer does the ECU have to wait until the exhaust gasses have heated it for it to start working properly.
It's a lot more efficient and cleaner this way.

But a lazy preheater caused my fuel status problem, it wasn't broken, otherwise it would have realised it was an open circuit, it just didn't heat fast enough for the ECU to trust it's signal, so it tripped into a preset, safe fueling status and caused an erratic, high and hunting idle when warm.

The downstream or post cat sensor works in the same way, generating a small electrical signal based on exhaust temps but the signal it generates is very different (if it ain't you have a Cat problem).

It's signal is hard to nail down because it does depend more on cat's temp, as the cat's performance increases with temp, but it's usual to see a much smoother "Switch" and a more even/higher/leaner voltage when the cat is at operating temp.

It also doesn't influence the fueling, it just monitors the cats performance, ie, it monitors/detects if both O2 sensors are the same, if they are, a cat performance related DTC is generated in the ECU.
I'd say Murfman, that your open loop post cat sensor problem was in fact a preheater open circuit issue, ie, the heater element was broken.
ECU's seem to detect if the heater element draw power, if not they report a open circuit problem, usually a broken element or a wiring issue.

Luckily with the Panda, both sensors are the same part.

Going back to the idle issue, it will hold on to rpm if the alternator and engine (air con) is loaded, it's trying to recharge your battery and run all this electrical equipment.

Try is again with everything off.

 

[matty23]

Hi,

Good news - however it doesn't make any sense. Drove the car all day today and then finally this evening and it all behaved normally!

I've added photos of the car idling. I even revved the car up to 1,500 rpm and it came straight back down to a nice idle speed.

Does the idle speed look correct?

Matt.

 

[murfman53]

Hi Goudrons,

Thanks you so much for a very comprehensive description of the 02 sensors and their functions. And taking the time, to put pen to paper so to speak, in giving an extremely enlightening account of how these sensors are so important to maintaining our cars.
Regarding my recent open loop post cat 02 sensor, you are perfectly right, the issue must have been a pre heater fault. I did replace it, and now works a treat. Even though I removed it and checked the voltage readings with a little heat from a blow torch, they seemed to be fine. Although, the ohms reading was a little high, this must have been the fault.
A lazy 02 sensor, therefore remaining in "open loop".
Again Goudrons, thanks a million for this vital information.
I think I'm in CLOSED LOOP now.

John

 

[matty23]

I agree Murfman53. Goudrons explaination certainly taught me a thing or two about modern day fuel injection systems.

It's most certainly invaluable information which I will use in the future if I need to. However, for now I believe my car is back to normal, not entirely sure what happened, but good to know if it occurs again I know what to do!

Matt.

 

[murfman53]

Hi,

Good news - however it doesn't make any sense. Drove the car all day today and then finally this evening and it all behaved normally!

I've added photos of the car idling. I even revved the car up to 1,500 rpm and it came straight back down to a nice idle speed.

Does the idle speed look correct?

Matt.

Hi matty23,

You must be delighted with your progress.......................and rightly so.

The idle rpm looks just a fraction higher at 800 to 850rpm. I wonder would it drop a liitle if you turn on your lights? Do you have a multimeter just to check the condition of your battery when things are running. I'd say its something small, but you'd like to get at the bottom of it all the same.
Idle air control valve, I believe controls your idle speed. Might just need another cleaning.

John.

 

[murfman53]

I agree Murfman53. Goudrons explaination certainly taught me a thing or two about modern day fuel injection systems.

It's most certainly invaluable information which I will use in the future if I need to. However, for now I believe my car is back to normal, not entirely sure what happened, but good to know if it occurs again I know what to do!

Matt.

Could not agree with you more. Detailed information is so important, and its great to be able to get it............................and do it yourself!!!

No expensive trips to the dealers.................Thanks to................... Goudrons!!!

 

[matty23]

Thanks Murfman,

I'm sure it's always idled around that figure, even when I bought it back in 2015.

I have attached two pics that were took prior to this issue. The first one is the dealer advertisement of the car (and you can see the instrument cluster earth fault which thankfully was later fixed under warranty) & the other one was about a year ago.

Matt.

 

[murfman53]

Hi Matt,
Looking closely at the pics you present above. I notice that the pic on the left, showing the rpm reading, looks very like a figure of 750rpm. I might be wrong in my assumption................or a visit to SpeckSavers!!!
The pic to the right, looks more like 850rpm or there abouts. The pic to the left also shows the petrol gauge on the low side. Of course if you less fuel in your tank, its safe to say, I suppose, more vapour. Its been said to me, if its true or not, always keep your petrol tank full or there abouts. The reasoning behind this statement, was that the purge valve would get less use, whereas a near empty tank would keep the purge valve very busy, because of more space for vapour. Now, how much truth is in that assumption, I really don't know for sure. Something more to think about.
Does your scan tool measure rpm at all. I mention it because if the scan tool shows 750rpm and your car instrument rpm gauge shows 850rpm. Its just a test you could perform to clarify and confirm your test results.

John.

 

[matty23]

I agree Murfman53.

It was a picture (the one to the left) taken by the dealership when they advertised the car, unfortunately they ran it pretty much dry!

My diagnostic tool is quite literally just a code reader which cannot perform more technically advanced jobs other than just reading or erasing codes. I wish it did do more though.

I'm going to see how it goes, as it may jump back to open loop.

Matt.

 

[matty23]

Hi,

Although my car is back to running ''normally'', as in it's no longer revving on its own and settles back down to idle when the clutch is dipped. I am finding that the idle speed does look (like Murfman53 suggests) a little high for idle speed.

Now, as far as I can remember (since owning the car from Jan 2015) the idling speed has been around 800rpm (maybe slightly higher, no more than 1,000). However, I've been comparing my idle speed from the pics with other Pandas for sale online and all appear to idle around 750rpm.

Although my car is driving and behaving normally and the idle speed doesn't sound fast, it's puzzling as to why it wishes to idle at around 800rpm and remain there (no fluctuations).

Now - I have checked the throttle body, air intake, disconnected the battery for 10 mins, disconnected TPS & IDC and cleaned the air filter. All of which I was hoping would allow the car to settle back down to 750rpm, but no, it happily remains there.

Is there a fault, or is this normal? No dash lights on and if I didn't check, I certainly wouldn't be any of the wiser. My MOT is on the 2nd August and I don't want it to fail over this minor issue.

Matt

 

[matty23]

Hi guys,

I've tried everything regarding the idle which likes to stay at 800rpm. I can hear the switch between closed and open loop during warm up and it comes from 1,400rpm, then 1,200, then settles down to 800rpm.

The car is happy to sit at 800rpm with no fluttering or hesitation. I cleaned the throttle body, adjusted the throttle cable, unplugged the battery for some considerable time, cleaned the throttle body (TPS, ICV, MAP) sensors.

No fault codes are stored, not that I expected there to be. I looked at some pics that I took before my last MOT IN 2015 and I noticed the car happily idled at 800rpm and it passed with no problems.

Any suggestions,

Matt.

 

[A3jeroen]

Is 800 really wrong? Maybe your tach is not as precise as you think. Might be 750 in reality.

gr J

 

[murfman53]

Is 800 really wrong? Maybe your tach is not as precise as you think. Might be 750 in reality.

gr J

Hi,

You have raised a valid point. I suppose the only way to confirm the idle rpm,

would be to connect a diagnostic tool, which would read the rpm.

John.