1987 - 1996 F150 & Larger F-Series Trucks 1987 - 1996 Ford F-150, F-250, F-350 and larger pickups - including the 1997 heavy-duty F250/F350+ trucks

High idle

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Old

Jul 23, 2015 | 04:57 PM

#1

Beardad82

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High idle

I've got a 92 F-150 with a 4.9L that I just finished putting a new set of lifters and pushrods in. Got it back together and turned the key and cranked like a dream but the idle is way high. I've unplugged the IAC and nothing changed as well as back the idle adjustment screw almost completely out. All my vacuum lines are in good shape. Anyone have any input?

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Old

Jul 23, 2015 | 07:23 PM

#2

rla2005

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From: Kentucky

Put the throttle stop screw back. You have a vacuum leak. Replace the vacuum lines. One or more broke, Very common problem.

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Jul 23, 2015 | 09:14 PM

#3

Beardad82

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I've checked all of my vacuum lines and they are all solid. If I unhook them the rpms go up even more.

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Old

Jul 23, 2015 | 09:22 PM

#4

rla2005

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From: Kentucky

Quote:

Originally Posted by Beardad82

I've checked all of my vacuum lines and they are all solid. If I unhook them the rpms go up even more.

Did you plug the ends?

The problem you describe is very common with broken vacuum lines. The vinyl tubing gets VERY brittle with age. Visual inspection may not work very well.

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Jul 23, 2015 | 09:42 PM

#5

Beardad82

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I did plug the ends with my thumb one at a time. I'll go back over them again when I get a chance

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