S3 with lumpy idle and random misfire on bank 1

[JohnDudley]

My 2001 AMK S3 is driving me nuts.

When you first start it, it runs fine, then within 20 secs the idle is lumpy, occasional knocks etc.
If you depress the throttle and run revs to 1100 it runs smooth.

On the road, I get a random misfire on Bank 1 (occasionally bank 2). I've had the coil packs and plugs swapped out for known working sets and the problem persists.

I've had someone look at this who as done some data logging and says the MAF, crankcase sensor and several other sensors seem to be working correctly. He said that one minute the engine is running perfectly, next it's misfiring, but does not know the cause.

Does anyone have any ideas on what could be happening?

Thanks
John

 

[aragorn]

Check the wiring harness to the coils. The cable insulation cracks up and can short out randomly.

 

[<tuffty/>]

Checked for the usual vacuum leaks yet? check block 032 after a run to see what the fuel trims are like...

You say you have logged stuff but what have you logged and under what conditions?

Spec and mods of the car? remapped? std?

Do you get a misfire under load (full throttle acceleration for example)

Not enough info yet to make much od a diagnosis but if the ignition side is deemed to be ok then you have fuelling which seeing as it only cyl 1 or 2 may not be the issue... the other thing it could be is component failure of some kind... headgasket for example, rings or maybe even a bent rod...

Stuff like this is trickier to diagnose but you need to eliminate the obvious first.. compression test, hydro carbon test and checking for split pipes etc being top of the list...

Road/dyno logging with VCDS to see what fuelling, boost and timing is up to under load too

<tuffty/>

 

[JohnDudley]

The car is a standard 2001 S3 AMK, I've had since new.

The data logging was done by sub11motorsport in Peterborough, said he had checked all the usual stuff but couldn't figure out what the issue was.

It does misfire more often than not when under load, throughout the rev range, if your gentle with the throttle then it doesn't happen too much. I was thinking clogged injector.

Thanks for the advice, I'll have a read through the vacuum leak thread and I'll get on with it over the coming days.

 

[towcestervag]

check vac hoses under inlet manifold
the one that goes to the breather splits and the connection is by no 2 cylinder
i must admit it usually throws up a missfire fault and lambda