Idle and Running Issue

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Oct 17, 2010 | 10:59 PM

ScorpionND

Thread Starter

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Joined: Oct 2010

Posts: 2

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Idle and Running Issue

I have an 87 F150 w/ 4.9 4 speed. The truck starts alright, but the idle bounces from high idle to low idle constantly. WHen I try to rev it up, it misses. I have tested many things, but can not find the issue. I did find that the engine idles very low, but evenly, if I unplug the MAP sensor (only if I leave the vacuum line open to ambient air). Is there anyone who can help?

Oct 18, 2010 | 12:36 AM

polarismuddman

Senior User

Joined: Aug 2010

Posts: 399

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From: Central, Florida

What exactly have you tested and/or changed on the truck? If you haven't checked the TPS check out the link for it in my sig.

Oct 18, 2010 | 06:30 AM

Duct Tape Racing

Elder User

Joined: Jul 2010

Posts: 960

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From: Saint Charles, Missouri

Quote:

Originally Posted by ScorpionND

I had the same problem with my 4.9 , it had a choppy ildle and fluctuated High to low but when drivng, it got up to rpms and drove just fine but if i Floored it , it seemed to not get enough fuel, at first I thought maf or vaccum leak but after testing it all I ended up getin a new head gasket and it was the reason it was sucking a small amount of air in and messin with the idle and running. May not be the cause for yours but it sounds like similar symptoms of mine so I figured I'd share