1.8T 2001 AUM Running Issues

[vdub1980]

Hi all i'm new to this forum so sorry for instantly asking for help but i'm kinda desperate.

I've had my car for 18 months or so and it's never run quite right. After replacing loads of parts it's much much better but i still have a slight problem.

The best way to describe the problem is that when im driving normally say in second gear, without pressing the throttle any more than a small amount there is a sudden surge of power and when i release the throttle completely to change to third the car sort of judders for a second. It almost hesitates very much like a misfire. The engine idle is ever so slighty rough, it drops and picks up but only a tiny amount. Also if i pull away and change to second with the revs very low the car sounds like the exhaust is blowing (and squeaks) which is very odd because it isnt? It passed the MOT fine. I can also clearly hear the turbo but the sound of it is muffled and not a clear whistle and sometimes but not often i get a small puff of blue smoke from the exahust (i can see in rear view mirror) but it doesnt happen all the time. Should I be able to hear my DV (whoosh sound) on a completely standard engine with no mods?

Last thing is when the engine is cold the engine fan kicks in for 2 seconds after ticking over for about a minute and goes off again but it doesnt do it at normal engine temp.

I've checked the whole system for air leaks and there are none. Intercooler looks brand new.

Iv'e replaced thise parts:

New MAF, lambda, coolant temp sensor, air temp senser, coil packs, spark plugs and i've cleaned the throttle body but the problem had nearly always been there before i took throttle body off.

Car has covered 131,000 miles now

NO fault codes when scanned with VAG nor is the check engine light on ..

Thanks for any input on this one!