Technical Punto mk2a High emissions

[crankshaft]

My Punto from 2002, failed the emissions test. I was told the CO was too high.
The emissions test is done in 2 parts. Part one with the car idling. Part two reving up the engine between 2000 and 3000 RPMS.
The CO was high in both cases.

The car drives fine, and idles fine.
However, at idle, when I rev up the engine, I can't keep the car at a fixed rpm value.
I can't keep the revs steady at 2500 RPM they start going up without inputting any change to the the gas pedal. And the ECU reports that it is in closed loop.
I connect MultiECUScan and I can see the throttle position increasing without any changes to the gas pedal, they start going up, then stop going up and start hunting around a value, and never stay steady.
I have no idea where to go from here, the car idles fine, which makes me think the throttle body is working good. It seems that the ECU commands it to open more, even though I didn't press the gas pedal more.
This only happens when the engine has no load. I went for a drive, with MultiECUScan connect, and I don't see any changes to the throttle position, that don't match the gas pedal.

I took 3 screenshots of MultiECUScan. One of the images is with the engine at idle. Two of the images are when reving up the engine to 2500 with the car at idle, that is stopped, no engine load.
The screenshots also show the lambda sensors status, and the ignition timing and throttle position.

Is there a relation between high CO levels - at idle and when reving at around 2500RPM - and this symptom also happening at idle that the engine won't keep the RPMs steady?
I don't know how to interpret the Lambda Integrator value.
I can see the spark advance goes negative when I rev up the engine, I don't know if that's normal.
The injection times seem very close, at idle, or when reving up, but I also don't know if they are high.

 

[crankshaft]

I should also say that I don't notice a high fuel consumption. The onboard computer reports 21km/L, and it does add up with how much gasoline I am putting in the tank.

 

[Mike1alike]

Accelerating on it's own is caused by vacuum leak. You can see it in the pictures you took, the "Air flow rate" is higher and having more air, the ECU tries to make a corect air/fuel ratio and that is why the RPM goes up.
You either have a crack in the (admission) intake manifold and that may refer to the manifold gaskets being worn out, especially those between gasket and cylinder head (4 of them, there is one for each cylinder) or you could have the case of faulty IACV.
This bad ratio mixture can be the reason the CO emissions test failed. After fixing the vacuum leak problem, you can do a cat cleaning, that will help with the emissions test and also, will help the engine run smoother.
For cat cleaning you can use 1l of vinegar. And you'll need to pour it into cat, hot engine, through the pre-cat O2 sensor hole. For that, is best you prepare the action while the engine is cold, make way (take down the thermal shield) and take down the O2 pre-cat sensor. Then put it back without tightening it up too much. Start the engine and warm it up. Stop the engine, take down pre-cat O2 sensor, pour the 1l vinegar into the cat using a funnel and beeing carful not to get burned (also wash the sensor with vinegar), than put the sensor back on. Then start the engine and run it at 2500-3000 RPM for about 10 mins. Your cat will be clean after that.

 

[crankshaft]

Accelerating on it's own is caused by vacuum leak. You can see it in the pictures you took, the "Air flow rate" is higher and having more air, the ECU tries to make a corect air/fuel ratio and that is why the RPM goes up.

@Mike1alike are you referring to the RPM going up with car engine idling?
The engine idles just fine. I don't see the RPMs going up. The problem I was describing happens when I rev-up the engine, by pressing the gas pedal, with the car stopped. I am not able to keep the RPMs steady, they start going up to about 3000 RPM, and they never keep steady, they start oscillating.

You either have a crack in the (admission) intake manifold and that may refer to the manifold gaskets being worn out, especially those between gasket and cylinder head (4 of them, there is one for each cylinder) or you could have the case of faulty IACV.

In the 1.2 16V Punto the throttle body is fully electronic, and there is no IACV.
If I had a cracked admission wouldn't I see the problem the engine idling?
I only observe the problem when reving up the engine with the car idling.
Maybe my use of the word idling is confusing things. I think a better description is, When revving up the engine with the car parked, I am not able to keep the RPMs steady. And it's impossible to make them stay between 2000 and 3000 RPM, the engine always goes up to above 3000.

This bad ratio mixture can be the reason the CO emissions test failed. After fixing the vacuum leak problem, you can do a cat cleaning, that will help with the emissions test and also, will help the engine run smoother.
For cat cleaning you can use 1l of vinegar. And you'll need to pour it into cat, hot engine, through the pre-cat O2 sensor hole. For that, is best you prepare the action while the engine is cold, make way (take down the thermal shield) and take down the O2 pre-cat sensor. Then put it back without tightening it up too much. Start the engine and warm it up. Stop the engine, take down pre-cat O2 sensor, pour the 1l vinegar into the cat using a funnel and beeing carful not to get burned (also wash the sensor with vinegar), than put the sensor back on. Then start the engine and run it at 2500-3000 RPM for about 10 mins. Your cat will be clean after that.

Will the vinegar be expelled through the exhaust? I am thinking that my cat does need cleaning. I am a bit scared of damaging it though.
What sort of vinegar do you use?

 

[Mike1alike]

Yes, the vinegar is expelled through the exaust, at those temperatures it is instantly vaporized. I did cleaned my cat this way and the first thing I noticed was better response while pressing the acceleration pedal, like no lag and also smoother running of the engine.
As for the other problem, the fully electronic throttle body does do the work of IACV and for sure the problem comes from the TB or the acceleration pedal. First you can clean them very well, there were cases of just oxidized contacts. If cleaning them doesn't solve it, you will need to replace the one that is faulty, the TB or the sensor on the pedal. I don't know exactly how can you figure out for sure which one is faulty, but I think some multimeter measuring could give you some pointers. Also, try first the cat cleaning and see how the engine runs afterwards, maybe you won't need to do anything on the TB.

 

[J4MALD1N]

I had a 1.2 8v Mk2b fail its emissions for the same reasons (CO). A bottle of Cataclean in the fuel tank and a good drive later to clear the cat out it passed. Maybe give that a try and see if it works.

Edit: If you struggle to find Cataclean, most Catalytic system cleaners from larger brands such as LIQUI MOLY should do the trick

 

[crankshaft]

Yes, the vinegar is expelled through the exaust, at those temperatures it is instantly vaporized. I did cleaned my cat this way and the first thing I noticed was better response while pressing the acceleration pedal, like no lag and also smoother running of the engine.
As for the other problem, the fully electronic throttle body does do the work of IACV and for sure the problem comes from the TB or the acceleration pedal. First you can clean them very well, there were cases of just oxidized contacts. If cleaning them doesn't solve it, you will need to replace the one that is faulty, the TB or the sensor on the pedal. I don't know exactly how can you figure out for sure which one is faulty, but I think some multimeter measuring could give you some pointers. Also, try first the cat cleaning and see how the engine runs afterwards, maybe you won't need to do anything on the TB.

I gas pedal only has 2 wires connect to it. I think it must work like a potentiometer. I can check it with a multi-meter, but since I don't notice any RPM changing when driving the car, I am not suspecting the pedal. But I will check it.
I am thinking the throttle body is fine too, I check and it is clean, no gunk or soot, I suspect the ECU is having problem keeping up steady RPMs when revving up with the car parked.

The CO levels where high, but the NoX and the HC where not. I am didn't pay attention to the lambda value of the car's emission, I remember seing 1.00 I can't remember all the decimals.
Is this a sign of a dirty catalyst?
@Mike1alike I feel a bit wary to pour a liquid in a hot lit catalytic converter. I don't have a easy way to make an adapter that will but the lambda sensor hole.

 

[Mike1alike]

I made an adapter using a hose, part of an old breather it was, I think, extended it with another slightly larger hose and at the end I've put a funnel. It worked really well.
It might be a sign of dirty cat, first of all due to high level of CO and also the difficulty of maintaining steady RPM. I think the ECU is making adjustments because of the out of order measurements it gets, so it pumps gas. This was an instant effect that I've got after cleaning the cat, no lag between the time I press the accelerator and the engine actually accelerates and the ease of keeping the engine steady at whatever RPM I want, with ghe car stationary, like 2000, 2500, 3000 RPM.
The lambda values look ok. The best is to select both of them and record a graph testing. They should keep between some limits, but they move mirroring one another, as you accelerate. The pre-cat is on higher voltage and when it moves up or down, the post-cat moves the same. If there are problemes with one of them, as I've said, you can easily spot it on this test.