I've been chasing a weird running issue with my parents 1.8T for a while now. I've tried everything i can possibly think of, but just aint getting to the bottom of it.
The original problem was really harsh juddering, mostly at low/medium revs with lots of throttle. You could plant the boot at 2500rpm and it would pull, then it would judder harshly (sort of like someone was turning the engine off momentarily)
I changed the Coils and ICM for spares, and it got slightly worse. I swapped my spare MAF in, and it stayed the same. I changed the plugs and it got marginally better.
Then i discovered a split hose on the inlet manifold, running to the PCV gubbins, ie a huge boost leak. Repaired that, and the cars much better.
However its still not right. At random it still judders. Much less frequently and much more randomly, but still happens. Also now, if you give it full throttle in fourth gear say, you can feel constant very slight hesitation. It doesnt just smoothly climb thru the revs, theres constant small judders, somtimes so slight it just feels like a slight reduction in power output momentarily.
I'm going to swap the coils with the ones off my own car, as i know for sure they're good, and i'm going to refit the original MAF sensor incase the one i've fitted is slightly dodgy and was masked by the boost leak.
Any other ideas?