Technical Intermittent lull in engine drive

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Technical Intermittent lull in engine drive

DTanner

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All,

I have noticed recently that my 1.2L Fiat Panda Dynamic Eco 2009 has an intermittent lull in drive. I believe this happens irrespective of whether the car is warm or cold and whether in a high or low gear.
For instance, if I am travelling on a motorway with the accelerator held in a fixed position it will suddenly shudder briefly (losses drive) and recover. When travelling at slower speeds or in heavy traffic this can sometimes lead to stall/cut-out of the engine.
It is pretty infrequent and I have not encountered it in the last two weeks but I would like to know why it occurs and how important or not it is that I deal with it. The garage want £100 just to read the error codes.

Has anyone else encountered this?

Regards,
DT
 
No.


Sometimes folks have had similar going over bumps etc - it can be dry connections on the ECU plugs (remedy is to pull them out a few times and/or clean the pins, lubricate.


I paid £15 for a code reader/reset on ebay, though you can get FIAT specific reader/reset software - MultiECUScan (MES).
 
An update on this. The intermittent loss of power has become more frequent and I need to do something about this.

Summary - the lull occurs at:
- any temperature
- any gear
- just after starting or on long journeys
- at high RPM or low RPM
It is very indiscriminate.

On a motorway the lull causes a short judder as the car loses power and then picks up again (there were no sounds that would suggest a misfire). At low speeds (because it is lower speed) the judder can be quite forceful.
I have not noticed any other symptoms, e.g., no electric gremlins and the car starts perfectly. The runs really well apart from this.

However, and it may be unrelated), yesterday while my wife was driving the engine stalled three times. It stalled each time when stopped at traffic lights and she did not notice the stall until the lights when green and the engine didn't respond. Following this the EOBD ENGINE CONTROL SYSTEM FAILURE light came on (solid - not flashing). It has since disappeared.

My thinking is whether the lambda sensor can account for everything and whether it is worth replacing. Any other possibilities? Any thoughts?

Thanks
 
If the light has been on while driving there will be a code stored. Might be unrelated or it might point you in the right direction (fault codes very rarely diagnose themselves, just let you know what's happened). Pick up a cheap EOBD code reader, or book it in at a decent independent for a code scan.
 
Thanks.

I have a reader ordered, that should arrive tomorrow. Will let you know what I find.
The challenge I am facing (which I guess is a common difficulty) is that I don't know how to track the symptoms down to something I can test or replace. I don't really know if one of the lambda sensors is at fault as everything seems to work well in other ways (i.e., the car appears to idle fine).

My current strategy appears to be:
- Selecting a random component
- Replace it
- See if it resolves the issue
- Repeat as necessary

This is a costly strategy (local suppliers of lambda sensors charge around £80 per sensor) but finding the areas to focus on is challenging. Hopefully I can get some guidance from the forum. Thanks.
 
Update:

I read the error codes on the car and found a single stored code, it is:
P0120 - Throttle / Pedal Position Sensor / Switch a Circuit

I have looked around the forum and net and these references appear to be the most relevant:
https://www.fiatforum.com/panda/248022-1-2-dynamic-throttle-position-sensor.html
https://www.fiatforum.com/bravo-brava/133158-new-tps-throttle-positioning-sensor-how-much-replace.html
Some of the symptoms appear similar to what I am experiencing.

Next steps are basically:
- Disassemble the throttle body
- Clean up
- Check sensor signal output
- Check and clean connections and air hoses

Will let you know what happens.
 
Sounds good, if you remove tommyoir air box and use appropriate cleaner, you should be able to degunk it in situ, be gentle when opening the butterfly. If you do take it off the car, make sure you take note of the seal, and don't crimp/bend/trap it when rebuilding, as that will cause an unwanted air leak
 
Just an update on this.

I changed both Lambda sensors and the juddering appears to have stopped (no signs for the last 3-4 weeks). I first replaced the pre-cat one then moved this to post-cat but didn't see a difference so replaced both and it looks better.

I also did lots of other stuff like cleaning contacts, cleaning the throttle body and even replacing the throttle body (with a £16 eBay version) but no success until both Lambda sensors were changed.

However, although the juddering appears to have disappeared I now have another problem. The car has a high-idle that I cannot resolve. Sometimes it is fine (starts cool at ~1,200 RPM and drops quickly to ~800 RPM when warm). However, other times it can start fine and following a drive idles at 1,500 RPM even when warm (and I can here the engine racing in idle) or starts cold at 1,500 RPM.

This occurs with either of the throttle bodies I have. I have noticed that there is some oil leakage around the throttle body seal (I cannot find a replacement seal) but nothing else that noteworthy.

Any ideas why this might be?
 
Try cleaning the ECU multiplugs with some contact cleaner (with battery disconnected).
It may be causing spurious readings from the throttle position sensor.
 
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Thanks.

I have cleaned the ECU contacts and ordered the crankshaft sensor.

Will let you know how it goes.
 
The possible CPS fault was just a guess!

High idle speed can be an inlet side air leak. Has anything been done that could cause a leak between throttle body and engine?
 
Hi DTanner, just check that the breather pipe that connects the rocker box, the inlet manifold and the air filter isn't misplaced or split. Last time I had my air filter box off, that pipe had hardened up and was in danger of splitting. That would give a nice air leak.
 
All,

The high-idle problem is either resolved or unnoticable now.

I removed the ECU connectors and they looked immaculate. However, I sprayed them with contact cleaner anyway, allowed them to air dry and reconnected them.

Since then I have noticed a single possible high idle (1,200 rpm) with a warm engine once in the last three weeks, though this was after a relatively short drive. This compares well with having 2-3 per day across previous months.

The car drives really smoothly now. So my experience is that replacing both lambda sensors fixed the intermittent lull and cleaning the ECU contacts resolved the high engine idle.
I also cleaned all sensor connections, replaced the battery, replaced and cleaned the throttle body. However, I replaced one thing at a time and did not notice these changes as helping.
 
A fast idle can be caused by an inlet manifold air leak between throttle body and engine. Check all hose clips and crankcase ventilation system for leaks. Also spray easy start around suspected area if revs change, up or down, you've found a leak. Ideally use a straw as given with WD40 or similar.

Air gets sucked in
ECU corrects the mixture
engine revs rise.
 
So still some problems with:
+ intermittent lull and high engine idle (which has been present on/off for the past two years or so). See original posts above. Every so often I get an error code from the car which is "P0120 Throttle / Pedal Position Sensor / Switch A Circuit". This has returned again recently.
+ Also recently I have noticed for the first time that I can rev the engine by pumping the foot brake

For the latter problem when idling in neutral I can pump the foot brake vigorously for a few seconds and get an increase the engine revs from 1,000 - 3,000 RPM quite easily. This seems to occur only when the engine is warm. Looking at live data on my EOBD reader the Throttle Position (%) is unchanged during this process. The only notable change in the data feed is spark advance which increases from ~25 degrees (at 800 RPM) to ~50 degrees (at 2,000 RPM). I have attached some images of the data feed. I could be paranoid but I think there is a hiss when the brake pedal is pressed, which comes from low down in the engine bay.

Also I have uploaded a video (see below) of the rev counter when the car is idling, which shows the needle fluctuating up and down (when the car is idling, so I'm not pushing the throttle).

[ame]https://vimeo.com/249953091[/ame]

I'm not sure if all of these symptoms are related.

Not sure what to do, but will look to:
1) Remove the throttle body and check for cracks/leaks in the black hoses and seal between the throttle body and engine
2) Clean contacts for ECU (have done this previously)
3) Clean throttle body (I have changed this previously for a £16 throttle body from eBay, with no change in symptoms)
4) Check and adjust the throttle cable to ensure good tension and no snagging

To try and help with these symptoms I have previously changed both lambda sensors, the crankshaft sensor, the throttle body (as the potentiometer is built in), cleaned the electrical contacts for all sensors I could find and the ECU connectors. Symptoms still present.

Any advice would be appreciated.
Thanks!

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What's the resting voltage of the battery after a couple of hours of not being switched on ?

Disconnect the battery and reseat the ECU connectors.
 
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I have had a quick go at the problem.

I checked the battery. The car was off and engine cold so I just put a multimeter across the battery leads and got 12.4V, which seems ok. I disconnected the battery and cleaned the ECU contacts. Then reconnected.

I removed the airbox and throttle body and inspected everything and it all looked ok to me. No obvious problems and hoses looked in good condition. Gave a quick rub down and reassembled.

I don't have a good process for trying to find a vacuum leak though. I have no propane (which I have seen recommended) so could do with some suggestions here. If there is a possible weakness it may be the gasket between the throttle body and the engine, this looks to sit very low in the gasket grove so leaves very little to compress. Is there a source to order a new one of these?

I also found a brake/reving problem like mine on the punto forum, where there is a very similar problem described, see:
https://www.fiatforum.com/punto-ii/429779-vacuum-leak.html

I have attached some photos in case you can see something I have missed. I have labelled one and hope someone can point me to the brake booster line (is it the one labelled 1?). I am focussing on these black hoses and the joints from airbox to throttle body and throttle body to engine. Is this reasonable?

Thanks.

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markup.jpg
 
What about the vacuum line going to the brake servo. Top right photo one.


Wd40 works well. You don't have to go mad. A quick squirt is all that's needed.
 
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