Hey guys first off I have a 99 built to 01 a4 quattro 1.8 t five speed. I have the airbag light of course and a check engine light saying cat below threshold. But every now and then I will get a cylinder 2 misfire now if I un hook the battery it will fix it till the next time it decides to do. Also noticed it only does it when I do mostly city driving.

 

Any takers?

 

Which cylinders? Same every time? If so it could be plugs or coils. Check the coil grounds on top of the valve cover - if one of the wires is bad, it could cause the issue. When does it happen? Under load, steady RPM, any certain temperature?

 

Thanks for responding I'm the devil. Its cylinder 2 and yes same everytime. New plugs and coils never follows the coil. Seems to only happen. I have checked the grounds just replace my valve cover gasket eveything looked good. When the car is at operating temp and I do a lot of city driving is when it does it, and it misfires at idle under a load and the only way to stop it is to shut the car off and unhook the battery for 5-10 mins. The more I've read on here I'm starting to lean toward an icm.

 

If it is always cylinder 2 & the coils & plugs have been swapped , try swapping the injectors. It might not be a bad idea to run a compression test also while your in there to give you the integrity on the engine itself.

 

^^^ agreed completely. Obviously air is getting there and coil/plug swapping didn't fix it, so it doesn't seem to be spark. Fuel is all that's left. An ICM issue is possible but from what I've seen/read it's more common for a bad ICM to misfire random cylinders than to cause it in the same one all the time (not that it's impossible). Before you pull injectors out, get some new injector o-rings to use. You don't want to risk a fuel leak on top of a hot engine.

 

+1 on swapping the injectors and running a compression test.

 

Thanks guys it was on my list to do guess its time to come out of denial that it could be injector or compression. But I've had a vehicle with injector problems and wasn't like this. I mean my car will go 2 maybe 3 weeks before it will do it again. And If I do all highway won't every do it.

 

I have also seen the ICM's causing misfires on these engines but you have to eliminate the other possibility's first.

As far as the injector swap , make sure the engine is cold , blow any crud away from where the injectors sit into the intake manifold & i like to use clear silicone spray for the injector seals for it makes for easier removal & installation.

Just remember is that you don't want too much silicone in the intake (not good for o/2 sensors).

 

Do you think a clogged injector would throw a cat below threshold code?