I recently did an engine swap as well as clutch, flywheel, headers and exhaust(nothing major, just another 13B) into my 90 GTUs. I had this problem before, but it wasnt as bad. (The problem) I start the engine, it runs fine, but if I hit the gas hard it hesitates hard, then it runs fine. If I accelerate slowly then I dont have any problems. Ive put so much money into it now that I dont want to turn back. We've replaced the fuel pump, mass air flow, and the fuel filter. We tuned the tps and everything but we can't get it to stop hesitating, if anyone could please give me some feedback I would really appreciate it. Im young (19) and can't really afford to put too much more into it, could someone please help.

 

are the injectors and fuel filter clean?

 

Ill try to check those today, but if anyone has any other ideas please help.

 

What year is that car???

 

Its a 1990 GTUs

 

yeah man i had the same problem two weeks ago!!
i hate that hesitant stuff man!!
it was my tps
definatly invest some muny and get a brand new one
the idle is good and turns on clean but around the 2800-4000 its ma hesitant
its the tps
just geta new one man

 

it already has a new tps, well.... I bought it back in march, so its almost brand new. Its just fine if I dont smash the peddle but if I need to get out infront of traffic or something then it hesitates and thats just not too safe. Im going to try to tune the tps again with my mech, Ill post more later. Thanks for all the help.

 

Tuning the TPS didn't help, were now replacing the front catalytic converter thinking that may be causing the delay. It has been hollowed out and perhaps it may not be getting enough back pressure... though it is an S5 motor and the 5th and 6th port dont open up with backpressure, if anyone else has any other suggesions please help because I am running out of funds, time and patience quickly.