Technical Punto MK2a 1.2 16V RPMs surging

[crankshaft]

Hey,

The engine idles just fine at around 900 RPM. And when driving I do not notice this issue. The issue surface about 3-4 years ago, and it has been plaguing my Punto ever since.

It is a Punto MK2a from november 2002 1.2 16V 80 hp. the throttle body is fully automated, and electronically controlled by the Engine ECU.

It's having this issue where when I press the accelerator pedal to rev up the engine, and try to keep the RPMs steady at 2000 (with the car parked), the RPMs start surging, and the engine revs up more and more, even though the accelerator input remains the same. Eventually theRPMs come back down just to go back up again.

I check both potentiometers in the accelerator pedal, even though I don't have any reference values, I do not see any changes that would justify the rev up of the engine - based on this I cleared the pedal as the culprit.

I thought it could be the throttle body, so today, I replaced it with one from a junk yard.
The problem persisted, although I think I noticed a slight improvement. Now the car only exhibits this issue when the engine is warm, but I need to test it further to confirm.

I am thinking I might need to trigger the ECU learning procedure for the new throttle body, but I do not know how to do it?
Is there a procedure for this?
I have MES (MultiECUScan) but there is no procedure for the ECU fitted in my car.

Any help is appreciated

The document, shared here in the forum, says the ECU implements the self-learning mode when the throttle body is changed. So, has it already taken place?

On another webforum someone listed this steps:

1. Disconnect the negative lead from the battery for a minimum of 45 minutes. Some people recommend overnight but that is not really necessary.
2. Reconnect the battery negative lead
3. Put key in ignition, turn to MAR and leave for 90 secs
4. Turn off the ignition, but not remove the key and leave for 90 secs
5. Start the engine but do not touch the throttle and let the car idle for 15 mins otherwise the car will not rev freely afterwards (as V6 owners know at their peril)
6. Turn the car off and leave for 10 mins
7. Start the car and take her for a blast

Not sure why disconnecting the battery could be a factor, since the Bosch Motronic says the data is kept even after the battery is disconnected.
I will try to do it and see what happens.

EDIT:
Chatgpt listed the following procedure, but it was unable to provide me with an sources, just said "I can't provide direct citations or sources for specific procedures. However, the throttle body adaptation procedure is commonly referenced in automotive repair manuals and forums for various vehicle models, including Fiat." - whatever that means.

To trigger the self-learning procedure for the electronic throttle body (ETB) on your Fiat Punto 1.2 16V, you typically need to follow a specific sequence of steps. Here’s a general guide on how to perform the throttle body adaptation:

Steps to Trigger the Throttle Body Learning Procedure​

1. Ensure the Vehicle is in a Safe Condition:
   • Make sure the car is parked on a level surface, and the engine is off.
2. Turn the Ignition On:
   • Turn the ignition key to the "ON" position without starting the engine. This allows the ECU to power up.
3. Wait for the Dashboard Lights:
   • Wait for the dashboard lights to illuminate and then go out. This usually takes a few seconds.
4. Press the Accelerator Pedal:
   • Fully depress the accelerator pedal to the floor and hold it there for about 10 seconds.
5. Release the Accelerator Pedal:
   • After holding the pedal down, release it completely.
6. Turn the Ignition Off:
   • Turn the ignition off and wait for about 10 seconds.
7. Start the Engine:
   • Start the engine and let it idle for a few minutes without any load. This allows the ECU to learn the new throttle body settings.
8. Test Drive:
   • Take the car for a short drive to allow the ECU to adapt to the new throttle body under various driving conditions.

 

[judderbar]

could be the temperature sensor for the water. I started my car one time without bleeding the air in the cooling system and the car raced uncontrollably in a very scary manner.

 

[crankshaft]

Today I tried all the methods that I could find to trigger a self learn. The results are the same, I am assuming the ECU has learned the throttle body position by now.

I notice something else, if I give the engine some load by turning on the headlights and the ventilation fan, the rotations become more stable, it doesn't surge like before, but it is not perfect.

Maintaining the RPMs is more difficult without a load on the engine. The throttle body position is a lot more critical in that situation.
I have already replaced the throttle body with a used one, what would be the odds of the one from the scrapyard having the exact same problem. I am considering this clears out the throttle body has a culprit.
Why would the engine ECU be opening the throttle, without an input from the accelerator?

Another thing I learned today is that the car failed, once again, the emissions test. Not sure if there is a problem with the catalytic converter and if that can cause the engine to behave this way.

(...) The issue surface about 3-4 years ago, and it has been plaguing my Punto ever since.
(...)Now the car only exhibits this issue when the engine is warm, but I need to test it further to confirm.

Could this be some sort of defect with a oxygen sensor?
I replace both sensors around 5 years ago, got them both from Bosch. I am not completely sure, but now I think the problems might have started back then.

could be the temperature sensor for the water. I started my car one time without bleeding the air in the cooling system and the car raced uncontrollably in a very scary manner.

Hi judderbad,

The sensor seems to be reporting correctly, at least the fan turns on in what seem to be the right times.
I can try to test it, maybe even disconnect it, and see what is the result, besides the fan entering full speed.
When you faced this issue, did the RPMs surge only when you pressed the accelerator pedal?
I don't think I have air in my system, but it doesn't hurt to check it.

 

[judderbar]

Hi judderbad,

When you faced this issue, did the RPMs surge only when you pressed the accelerator pedal?

I was not touching the accelerator pedal at all.

 

[crankshaft]

Hey,
(...)

I am thinking I might need to trigger the ECU learning procedure for the new throttle body, but I do not know how to do it?
Is there a procedure for this?

Today I noticed that MES lists this procedure to trigger the self-learning of the throttle body

1. Turn the key to MAR and keep it in this position for 60 seconds;
2. Turn the key to STOP for 15 seconds;
3. Turn the key to MAR and check that the idle self-learn has been completed correctly through the parameters found in the selection list. - Using MultiEcuScan. Warning: Pedals must not be pressed during this procedure.

 

[crankshaft]

Good news.
After some driving cycles, I am gonna say about 4-5 days didn't wrote down how many time it took, the throttle is normal.
I tried the learning procedures, but I suspect the ECU needed some drive cycles to fully learn the new throttle body behavior.

The RPM problem is fixed, it was the throttle body in my case.