Alright, so my car has the infamous hanging idle. It eventually reaches to about 800 RPM during idle but it takes like 10 seconds to do so. It also hangs in between shifts, so I did the IAC restrictor plate mod. My RPMs now drop immediately in between shifts, but hang around 1200 RPMs during idle and never return to normal. While it was idling I unplugged the connection to the IAC and nothing happened. To my knowledge it should either drop RPM or die when unplugging the IAC. The holes in the IAC restrictor plate are 1/4". Any ideas to get my idle back to normal. Bad IAC?
did you also try to unplug the MAF while it was running too. IMO the IAC restrictor plate is a BS fix for something else wrong. The car idled fine when it was new, mine idles fine now with 200,000+ miles.
Try testing the TPS to see if its at .98-.99 volt, it should just be under 1.00 volt. I heard that if this is out of wack you can get a wacky idle. I'm about to install my 75MM TB and Plenum so im going to find out soon. http://www.latemodelrestoration.com/products/Mustang-Throttle-Position-Sensor-TPS-Install-Adjust Actually I just did some further research and people are saying that the TPS is non-adjustable in the 96-04 cars.
I experienced your exact symptoms when I had my Saleen. I replaced the IAC with some brand I forget, it helped a bit but still didnt feel right. I eventually replaced it with motorcraft and it went back to normal.
Thanks for this info. I'm going to clean mine I've been getting a really low IDLE. They say when the IAC has systems it has low idle or it surges in neutral/park.
