high idle
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Trailering
Joined: Jul 2020
Posts: 21
Likes: 0
high idle
idle on my 88 f250 5.0l recently decided to "live" at about 2500rpm!!- when it first started i was able to kick it down with a burst to throttle- over the course of a few days, problem progressed to point that no longer works- mechanic who has been good on lots of other things checked idle motor and ran a smoke check for vacuum issues- both negative- any ideas?- thanks, guys
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
First thing to do is figure out if it is mechanical or electrical, so with the engine off..
1. disconnect the intake tubes from the TB and ensure the throttle blades are closing properly, exercise the linkage while observing how smoothly everything operates and if there is play in the pivot shaft anywhere. If it doesn't move smoothly or hangs up disconnect the cable to figure out of the problem is the cable or TB, and replace those parts as necessary,
If that all looks fine Start the engine..
2. one at a time electrically disconnect the IAC and TPS, make sure they aren't both disconnected at the same time.
Idle speed should drop with the IAC disconnected, but if you get the same result with it connected and the TPS disconnected the the TPS is the problem.
If disconnecting the IAC is the only thing that affects idle speed you have a wiring short or a faulty PCM.
If neither one of these makes any difference you have a pretty serious vacuum leak, it could be an intake gasket, a leaking brake booster, an EGR valve that is open to air, and a few other things.
1. disconnect the intake tubes from the TB and ensure the throttle blades are closing properly, exercise the linkage while observing how smoothly everything operates and if there is play in the pivot shaft anywhere. If it doesn't move smoothly or hangs up disconnect the cable to figure out of the problem is the cable or TB, and replace those parts as necessary,
If that all looks fine Start the engine..
2. one at a time electrically disconnect the IAC and TPS, make sure they aren't both disconnected at the same time.
Idle speed should drop with the IAC disconnected, but if you get the same result with it connected and the TPS disconnected the the TPS is the problem.
If disconnecting the IAC is the only thing that affects idle speed you have a wiring short or a faulty PCM.
If neither one of these makes any difference you have a pretty serious vacuum leak, it could be an intake gasket, a leaking brake booster, an EGR valve that is open to air, and a few other things.
More Turbo
Joined: Apr 2018
Posts: 729
Likes: 59
From: pine city washington
my problem on mine i think was the lower intake manifold. 4 of the bolts were tight the rest were finger tight and there was about 1/2 inch of oil and grease all over. got the old intake off, as soon as possible i am thinking about removing heads. the truck got hot enough to blow the rad cap off and it always ran at about 2500 to 3000 rpm.
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