A while back, I bought a rebuilt, ported to 52mm tb. I installed it, reuising gaskets and all, and car started to shift weird. It shifted early, and soft. I took it off a couple weeks later, and put stocker back on, stock gaskets and all, and car shifted fine. Since then, ive adjusted the idle screw, so when I let off the gas, the butterfly wont hit the openings. What could of been the problem w/ the shiftpoints. Now that I adjusted the idle screw, and got new gaskets, will that effect anything? I posted this a while back, and didnt get any answers why a 52mm tb, would change, and soften shiftpoints. Anyone?
(dont think it was tps. Shifted fine with the stocker reinstalled)

 

No it won affect anything even if you adjust the screw the computer compendsates and learns, it will be fine..

 

The larger tb lowers trans line pressure causing your weird shifts.To fix this you will need a tune to change the shifts.Assuming you have the 4l60e A4.You will not have this problem as log as you use the 48mm.

 

To correctly set the idle stop screw, you need to watch the RPM, IAC counts and TPS voltage with a scanner. While the PCM can usually correct the idle speed if the screw is set incorrectly, it may not provide the full range of IAC control for all operating conditions, and can throw the TPS voltage off far enough to cause a code.

 

Im going to watch with a scanner next time I install. Also, ive heard the tranny line pressure problem, but I always see in peoples sig 52mm tb, and never hear any threads on shifting problems, or computer tuning. Wouldnt you have to increase pressure on the 4l60? I have a 94 with the 4l60e. Not sure, I just dont understand why this topic rarely comes up, or why I hardly ever hear of people w/ throttle body problems. Did everyone that put a 52, or 58mm tb have to tune for line pressure?

 

You have to tune pcm for bigger TB or else you will fry the transmission.

 

mail-order tune man

 

The reason you don't hear people talking about the shifting problems that much is because alot of guys have m6 transmissions and you don't have this problem with a manual.I had my pcm tuned by madz28.com you could also have it done by pcmforless.com. You might as well get the preformance tune package and pick up a few hp if your going to run the larger tb.But there is really no need for a larger tb unless you have cam/Head upgrades or you're planning on a heads and cam .You will get much more out of a mail order tune than you will get out of that 52mm on a bolt on car.The mail order tune is the best bang for the buck mod I have done on my car.