Iac Question
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Freshman User
Joined: Mar 2004
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Iac Question
Got another question. 1987 f-150 4.9. I get a real fast idle, almost up to 3000 rpm. I unplugged the IAC vavle and the idle dropped to 1000 to 1100 rpm when warm. When cold I have to keep on the gas for a minute or two. I believe I narrowed my problem to that part. I was wondering if there is a way to clean this valve to get it to work properly again. Trying to keep it as cheap as possible. The truck is a beater with other kinks to be worked out too, but I love it. Thanks for the help.
Junior User
Joined: Apr 2004
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From: west virginia
Dont get mad at me for saying this but the best thing to clean these parts is only found at gm dealer it is called top engine cleaner in a blue spray can. I know I should not mention gm on a ford site but that stuff really works
Laughing Gas
Joined: Mar 2003
Posts: 877
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From: Colorado, U.S.A!
Originally Posted by judge1971
Dont get mad at me for saying this but the best thing to clean these parts is only found at gm dealer it is called top engine cleaner in a blue spray can. I know I should not mention gm on a ford site but that stuff really works
Laughing Gas
Joined: Mar 2003
Posts: 877
Likes: 1
From: Colorado, U.S.A!
If the IAC is not closing all the way because it's sticking or something, it could cause that, but you're right, it could be a vacuum leak. TPS is another possibility.
Hey, svdweb1, how you doing with that?
Hey, svdweb1, how you doing with that?
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Laughing Gas
Joined: Mar 2003
Posts: 877
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From: Colorado, U.S.A!
I guess I've read different books. My understanding is that you don't mess with the throttle stop screw and that the engine should either idle real low or die with the IAC unplugged. The idle speed is controlled by the computer with the IAC. 
Lead Driver
Joined: Nov 2002
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From: Concord, NC
I've heard that too, mainly on this board. I've set it both ways, and both ways seem to work fine - as long as the idle tps voltage is at the correct value either way should be ok I guess. The way I understand it is that the IAC can bump the idle if needed (a/c, cold start, etc), but it shouldn't have to hold it up just to keep the truck running. Best I understand, the IAC should normally be closed at idle.
Senior User
Joined: Apr 2004
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Here's an excerpt from the service manual:
"6 Shut engine off and install a specified feeler gauge between throttle return screw and throttle lever.
7 Disconnect the Idle Air Control (IAC) solenoid.
8 Start engine and run at 2500 rpm for 30 seconds.
9 Place automatic transmission in PARK, manual transmission in NEUTRAL.
10 Set idle rpm to the range using tachometer. "
"6 Shut engine off and install a specified feeler gauge between throttle return screw and throttle lever.
7 Disconnect the Idle Air Control (IAC) solenoid.
8 Start engine and run at 2500 rpm for 30 seconds.
9 Place automatic transmission in PARK, manual transmission in NEUTRAL.
10 Set idle rpm to the range using tachometer. "
