Weird Idle Issue

[87WhiteStang1]

Okay need some advice guys. my car has the weirdest idle. When i rev it or when i am driving and then put it in neutral and let off the gas, the idle will sit up pretty high for a few seconds then crawl down very slow to about 1000. If I am cruising in 3rd gear at 2 grand and put it in neutral let off gas the tach will imeadeately jump up to about 2200, sit there for a second then go down very slowly to about 1000. The weird thing is if I tap the gas pedal slightly right when it starts to do this the idle will imeadeately drop down to about 700 then back to about 900 and sit there. sometimes it goes lower and stalls. any suggestions would be great. thanks

Mods in sig.

 

[Tanus]

thats a common issue for modded stangs, search the 5.0 tech stickies for the "idle checklist thread"

usually its from dirty IAC valve