hi everyone I have a huge idle issue... my 1994 mustang gt with a 5.0 v-8 idles around 1800 rpm in park but every other gear is fine. I have replaced my IAC valve, PCV valve, MAF sensor and even tried messing around with the idle screw and throttle body stop screw and none of these things have solved my problem... someone please help me with this. thankyou

 

I have the same problem, im not sure if you tried this or not, But Try cleaning the IAC they have the directions on yahoo!

 

DIY KOEO/KOER/Cylinder Balance Self-Test

 

It could be a bad Idle Air Control motor I'm not sure if that is exactly what it is called but it should be near your throttle body.

 

is there a check engine light? is it possible that the eec thinks the car is cold? maybe a bad ect sensor?