Hi everyone,

I have a Skoda Fabia with a 1.2 AZQ engine. I have a warm running issue - the car misfires/stutters when fully warm. The intake air temperature (IAT) reads around 80°C when the problem occurs.

When I unplug the EGR connector the car runs perfectly and IAT drops to around 30°C.

Parts already replaced:

• EGR valve (new) + adaptation done

• MAP sensor (new)

• Coolant temperature sensor (new)

• PCV valve (new)

• EGR pipe is clean, no carbon buildup

Breather hose between EGR and air filter housing is intact

The problem existed before the EGR valve replacement as well, so the valve itself is not the issue.

I suspect the ECU is incorrectly controlling the EGR valve opening, causing too much hot exhaust gas into the intake manifold.

Has anyone experienced this issue on the AZQ engine? Is it possible to deactivate the EGR via VCDS coding? If so, what are the exact coding values?

Thanks in advance!

Have you inspected the brake servo vacuum hose for cracks and leaks?

2 minutes ago, Breezy_Pete said:

Have you inspected the brake servo vacuum hose for cracks and leaks?

Hi,

Yes of course. I checked these in every possible place. The interesting thing is that the problem only occurs when the engine is warm. The car works perfectly with the EGR connector disconnected. As soon as I reconnect it, the jerking starts after a few km...

EGR flow isn't enabled until coolant temperature is above a certain point, maybe 50°C, Can't remember exactly, so that may be why it's OK when cooler.

I'm completely at a loss. I have no idea. For now I'm using it with the connector disconnected but it would be nice to find out what's causing this. The shock came when I replaced the EGR with a new one and the error remained the same.

Can you try running without engine cover/airbox for a short drive when engine is fully warm?

See if fault still happens.

Okay, I'll try it. What I tried was to pull off the EGR rubber tube that goes to the air filter housing. Unfortunately, that didn't change anything. There's only an error if the EGR is connected to the system. As soon as I remove it from the formula, everything is perfect.

Are you aware of the warm/cold air mixer system within the airbox?

When the wax thermostat in there fails, it leaves the mixer flap in the 'maximum warm air' position.

The combination of that unnecessarily warm air and hot EGR flow may be causing the problem.

I don't know. Where exactly is this located? Can it be replaced? This could be a logical explanation

It's in the front half of the airbox, the section that does not need to be removed to change the filter.

Wedging the flap in the cold air only position is probably the easiest solution, which can be done with a screw.

Do the experiment first (running without airbox), I might be completely wrong about why the engine is having trouble.

Okay. I'll check it out. Thank you!

Unfortunately, this test did not yield any results either. IAT temperature is still above 80°C.

Does the engine ECU log any fault codes for EGR or anything else?

No. There are no error codes.

Another possibility, I guess, is that the catalytic converter is blocked to some extent, causing the exhaust pressure entering the EGR valve to be higher than mapped.

The feedback system for EGR opening is based only on physical distance, via a potentiometer in the top part of the valve.

So more gas could be flowing through EGR into inlet manifold than expected, causing higher intake temps and poor combustion.

How many kilometres has the car driven?

The catalytic converter was replaced not long ago. It's not because of this fault, but it's new. The car has 264,000 km on it.

OK, I give up.

☹️

Ok. Thank you for your help so far!