20lemons

I have 1994 mustang gt with a cold air intake, bbk 70mm throttle body and exhaust. I've been having this problem where I'm driving through town and I let off the gas the car stays at the rpm and doesn't come down unless I tap the gas again. started happening after I cleaned the throttle body. I've replaced the iac and tps still nothing I've even got a block off plate over the iac thinking that would help still have the issue. should I go back to the stock throttle body and see.

imp

Check the return spring which closes the throttle plate. Also, remove the spring and move the throttle plate by hand with your fingers, feeling if the plate closes smoothly and easily down to the stop. If there is any binding, it must be freed up.

20lemons

It is not binding it only gets stuck open when the car is on. I found out that if I unplug the computer chip to set the timing on the car and leave it unplugged it doesn't get stuck open but driving down the road with it unplugged makes the car misfire so I have to have it plugged in.