My car is idling around 900rpms warm in neutral with the vent off. I'm thinking the IAC has stopped working, I took it off and cleaned it out and it didn't fix the problem. Earlier today I unplugged the IAC when the car was running and the RPM's dropped down to about 650-700 and was pretty stable. Just a few minutes ago after driving home I unplugged the IAC again to see if it did anything different and it did nothing. The RPM's stayed at about 900. Should I try plugging the hose running to the IAC and see if it does anything different? I pulled the IAC hose off and held my thumb over in inlet tube and I could feel a little bit of suction when I revved the car but since I was not in the car I don't know if the RPM's changed any. Any ideas? Thanks
Oh, I did search!
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Chrome Yellow 1998 Mustang GT, K&N intake, 3.73 gears, PI intake, t-3650 trans, Mcleod super street pro clutch, Hurst billitt shifter, Bilstein shocks/struts.
(Loaded PI heads sitting in my garage for when I have free time )
(forged short-block in progress)
Eh, just replace the IAC. I cleaned mine, but the car still didn't run as well as it did with a new one. 900 does seem a little high, nothing crazy though. My car idles at 550-650, but that's because of my tune. I think vacuum leaks will cause a lower idle and stumbling, and the MAF MIGHT be the cause, but I'm really doubtful. You'll know when your MAF is not working right(car runs for **** when coming off a stop). Because it's doing this at idle, my bet would be to just replace the IAC.
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99' Rio Red Mustang GT:
Summit O/R H, MAC Flowpaths Turndowns, BBK Shorty Headers, Steeda UDP, K&N FIPK2 intake, Diablosport Delta chip, BBK 75mm throttle body, Trickflow upper plenum, Intake spacer, H&R SS springs, Cross drilled & slotted rotors, "Functional" hood scoop
I checked all my vacuum hoses and they look fine. Cleaned my MAF but like you said, I doubt thats the problem. Sometimes the idle is kinda erratic so I guess it can't be anything other than the IAC. Would you guys buy a Ford unit or something like a Duralast stocked at the local autozone? It just started idling a rough also. The plugs and wires are about a year old. I think I should go ahead and replace the coil packs as well.
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Chrome Yellow 1998 Mustang GT, K&N intake, 3.73 gears, PI intake, t-3650 trans, Mcleod super street pro clutch, Hurst billitt shifter, Bilstein shocks/struts.
(Loaded PI heads sitting in my garage for when I have free time )
(forged short-block in progress)
High idle, HELP! 
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