recently picked up another 98 gs3 for my girlfriend. its got a hesitation i havent been able to figure out. at around 2800rpm you can feel the power kinda fall off. it stays in this area of no power till about 3400rpm then takes off like you flipped a switch and added 100hp. no CEL, no codes. have replaced the maf, front o2 sensors, fuel pump ecu, engine ecu, cleaned OCV and screen, checked for post maf air and vac leaks and timing belt alignment. nothing has made a bit of difference. the fuel trims are 25% at idle on banks 1 and 2, and this number decreases as you get into the throttle, and are at zero when the power falls off, and do not change when the car takes off like it should. tps and maf values are all fine. not sure what would cause a lean condition that wouldnt trip the cel light, nor can i find anything that would cause it. when the power falls off it feels lean as hell, but without a wideband i cant verify what the afr's are. unlikely its plugged cats, cause it wouldnt start running correctly after 3400.
any ideas of other stuff i can try? ive got a whole parts car and spare GE engine sitting here i can take stuff off of to try, although other then the throttle body and injectors theres not much left. no misfires, car runs great other then this problem.
Mike

hmm.
-change pcv valve.
-clean throttlebody
-try running fuel injector cleaner through
-try new tank of gas.

This sounds like textbook MAF sensor. Try and clean it with some MAF cleaner. Although on a handheld scanner, your MAF values may look correct, they are not fast enough to catch the glitches many times. You would have to back-probe the MAF with an oscilloscope to catch them in most instances.

He says in the original post he replaced the MAF. But if he replaced it with one off his parts car it may also be dirty.

I'd swap a known good throttle body on and see if that makes any difference.

i had tried 2 different maf sensors with no improvement. also checked all those other things listed and that didnt help. i ended up swapping the throttle body assembly last night cause it was the only thing i hadnt changed, and low and behold, the problem is gone. much better overall throttle response, so im guessing it was on its way out.

There's my ego boost for the day. TYVM

I have the same problem but it doesn't happen all the time. Glad you posted this....I am going to check the throttle body. About a month ago I cleaned the MAF and the throttle body and had MUCH better throttle response with no hesitation. But now its back.