I put a new tb and pleumn on my 96 mustang gt and never new I had to adjust the TPS. My car idles high somtimes. Would this make my car slower and how do I adjust it.

Mods:70 mm pleumn,tb,cai,steeda udps,4:10's,and superchip programmer,mac catted h pipe,and magnaflow catback.

 

I'm not sure about the pre-99 stangs, but you need to check the TPS voltage. The voltage should be around .97-1.0v....I used my Predator to check the voltage when I did TB & plenum swap on my 03 GT. In order to adjust it to get a different voltage you just move the TPS around a little bit. It sounds weird, but the TPS is so sensitive that's all it takes.

 

on our cars, TPS voltage is reset/adjusted each time you start the car.
.900 to .999 is an acceptable range wth .990 being the preferred setting and higher voltage above .999 will give a high idle. now you can "slot' the screw holes to get a finer adjustment but most likely the problem is wth the aftermarket thrttlbdys being out of spec.

 

that's usually the nuts and bolts of it. there is a bit of tuning work to make up for the larger TB. High idle has many many possible causes including vacuum leaks, tune issues, IAC stuck open/sticky, dirty MAF... it goes on. Start by checking your TPS voltage and we'll take it from there.