Technical Punto Mk2a inconstant acceleration

[crankshaft]

Punto Mk2a Engine Surging

Hey,

My Punto 1.2 16v from 2002, has 2 problems related to the engine, and I am not sure if they are related, or not.

The CO emissions are a bit on the high side when the engine is idle. The car idles fine, there is no rough idling.


If you press the gas pedal, the CO emissions go up, and are slow to come down, but something else happens, you can't keep the car at a fixed RPM value, like 2000 RPM, it's almost impossible to do that.
Without moving the gas pedal, the RPMs start going up to the 4000's and then start coming back down, and repeating that.
Sometimes it will behave fine, and will be steady at the 2000RPMs, and it's easy to make it stay at a fixed RPM value, has you would expect.


Anyone has any ideas what could be going wrong with my car?

I have no idea when this started, because the car idles fine, and it drives fine.

When actually driving, the RPMs stay steady, and I don't notice a thing, there's no RPM hunting or loss of power or hesitation.

The fuel consumption information shows about 20km/l which is good for this car. I don't notice it consuming too much fuel, but I would have to test that out better.
The reason I noticed this was because they warned me about it in the annual inspection, MOT in the UK.

 

[Mike1alike]

It sounds to me that you are experiencing the problem I went through this summer, early stage in your case.
The fault is IACV (intake air control valve), it's malfunctioning intermittently. So, it has moments when it works fine and moments when it remains open. And the ECU corrects the fuel/air ratio, so the engine is revving up. But then the sensors indicates the engine should work in idle mode, it enters to idle fuel amount injection, but the air is again more due to the opened ramaind IACV and it does that on and on again.
Here is what I've been through with this problem:
https://www.fiatforum.com/punto-ii/488092-engine-revs-2000-rpm-idle.html
Of course, you should check for other air leaks, cracked hose or something, but my guess is that the IACV is the culprit.

 

[crankshaft]

In my case, if I try to rev up the engine, with the car parked, I can't keep the engine speed steady. It will keep rev'ing up, and slowing down, and it won't stay steady.

However the car idle's perfectly, I don't notive anything at idle, it's only when I step on the accelerator with the car parked.

Do you think it can still be the same problem has yours?
With your car parked, when rev ing up the engine it was impossible to keep it at a fixed engine speed like 2000 RPM?

My Punto is the 1.2 16V and I don't think it has a IACV, it has a throttle body that's electronically controlled.

 

[Mike1alike]

Yes, I think the same problem could be at yours, but if you have electronically controlled TB I'd say you should check that first and make sure it works fine. I'm guessing yours does have an IACV too, the electronic control of TB just replaces the acceleration cable. But verify that, I might be wrong.
And in regard of what was going on with my engine, the IACV had moments when it was working good and in those moments, of course, I could maintain it on steady rev. It started going wrong out of a sudden while driving and at first it would work fine if I would restart the engine. Then, more days and more drives passing by, and the problem became almost permanent, it had rare moments when engine ran fine. While IACV was not working ok I could't keep the engine on steady rev on idle, I thought at first that while driving it runs fine, but I realised that it did the same, just it was kind of hidden due to the fact of pressing the acceleration, that would cover up the problem.

 

[Mike1alike]

@crankshaft how are things? Did you fix the problem?

 

[crankshaft]

Hi,

I am still facing this problem

 

[Mike1alike]

Sounds like the problem is caused by a vacuum leak. Replace the inlet manifold gaskets and check if the breather hose is cracked.

 

[crankshaft]

I suspect it might be around the injectors, but I will try to look for it using ignition spray.

Sadly the car had the timing belt snap recebtly. I am waiting for a meachanic diagnose. But idk, this engine is probably interference, so the damage could be big

 

[Mike1alike]

Wow! Sorry to hear that. And yes, I think that engine is interference. But even so, the damage could be not very big. Like fixable! Good luck!