AFN strange problem

[oldskool rich]

ok so a mate brings me an A4, says its down on power, says he wants me to change the turbo, so i swap the GT15 for a GT17 as thats all i had knocking about, anyway the problem is still there, infact he says its much worse, its realy slow to rev, like it takes about 5 seconds to reach the red line wen reving in neutral, any ideas? i thort it cud be a boost leek but surly it wud still rev? cud be a colapsed cat but it runs the same with no down pipe, is there a sensor or vacuum pump that could cause this? why would it be worse with a GT17 i thort it would be better?

im out of answers, dont know much about the controls around the AFN, if anyone can help would be greatly appreciated

[rallydiesel]

Seems MAF-ish to me. Is AFN like a ALH? Sorry I don't have any more helpful advice.

[oldskool rich]

its 1Z, early TDI

why would having a better turbo make it slower?

[lucasone]

I agree, sound like a mass air flow sensor problem. The reason the GT17 would make less power is because a turbo spools up and makes boost based on how much exhaust is going through it. With a small amount of exhaust going through the manifold, the GT15 would actually spool up sooner and make more boost than the GT17. If you have a faulty MAF sensor the computer will only recognize a small amount of air going into the engine, so it will only allow your pump to inject a small amount of diesel. It's almost like you are giving 1/4 throttle.
Is the MIL light on? Do you have a scaner to check for codes? A faulty MAF sensor won't always set a code but if it does, then you know for sure that is your problem. Hope this helps, with out hearing or seeing the vehicle its hard to diagnose.

Cheers.

[superspringer]

Throttle position sensor mis reading?