when I let off the gas in my car it goes straight to 1000 rpm... then slowly settles to the actual idle... so I took off the IAC and sprayed it out and stuck it back on. seemed to be better but not perfect. this was a few days ago... today it is staying at 1100 rpm when you let off the gas but if you unplug the IAC while its running it settles right to idle. crank it with it unplugged and it dies when you let off the gas. am I to assume the IAC is bad?
Idle Air Control question...
- Thread starter kingcobracustom
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I agree, the IAC is bad. I recommend buying a Motorcract IAC - I've had troubles with every non-Motorcraft one I've bought. I'd also recommend going through this walkthrough and adjust your idle - your engine should idle at startup with the IAC unplugged. The IAC is there mainly for when the A/C is on at idle or similar load-at-idle situations. If your car won't idle without the IAC the idle setting isn't right.
R.J.
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Zero_chance
Founding Member
Just chiming and agreeing with the advice given. Especially on going with the motorcraft replacement. The idle reset procedure works great too. I did it after I bought my car because it used to randomly die when I put it in drive. Reset the idle and it hasnt done it in nearly a year.
Before I reset my idle, my GT's idle was really low - around 550 RPMs, and would threaten to die now & then. It also would fall flat on its face for an instant when I moved off the line, then jump to catch up. And it seemed to run rough overall. After resetting the idle, the engine purrs at around 650 RPM, nice & stable. It's quiet, too - if it wasn't for my exhaust I'd have to check to make sure the engine was running. Off the line it's crisp and responsive. Resetting the idle is really easy to do and every V8 Mustang owner should do it. 
Tom95gt
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Zero_chance
Founding Member
The IAC is pretty important during cold starting. On my 88, the IAC failed partially open so my idle was near 2000 RPMs so I made a plate out of aluminum with holes drilled in it to allow air to enter through the IAC and into the engine at a predetermined amount. Worked fine for me, but I only drove the car to and from work which was a few miles. I was selling the car and didnt want to spend the 60 dollars on a new one. This was before I started my second job too. I would definitely get a new IAC if this is your daily driver or even something you drive on a regular occasion. Definitely go Motorcraft.
I had this same problem on my '89 GT 5.0 did the usual clean throttle body and IAC, ect.. eventualy I started back at the basics and concidered what would really be the simplest solustion and started to look for cracks in my vacuum lines of course I eventually found it and problem solved $0 spent. I know if it went into a shop they would have gouged me for big $ and alot of unneeded parts. Skip to last week now my 2002 GT is rough idling and high idling when I let off the gas for about 15 secs (while I'm moving at any speed). Now my 1st plan of action was to read scan codes witch was my 1st mistake it pointed me to a lean system and bad O2's. But if you look at FORDs tech sheets on how the OBD II flow chart works, it will skip some tests if components before that test have failed or didn't respond. So more than likely you get incorrect readings. So I read the forums and saw that everyone jumped on the IAC and O2 replacement bandwagon with poor results. So for me it was back to my original plan of simple but most important vacuum leaks and I came across a tech sheet that was not aimed at my car but had a truth to it for all cars, it suggested to hose clamp on the pcv valve connections on all connections, I was in the process of this and found my large hose from passenger side pcv to TB was cracked along the bottom. After replacing it and clamping all other hoses my car purrs at 550 rpm (automatic trans) improved 2nd gear slam and all around drivability. So first check fuses then vacuum for any engine rough running condition they cost you nothing.
any suggestions on where to get it cheaper?
R.J.
Member
R.J.
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