4.2l intermittent idle
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Joined: Mar 2011
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4.2l intermittent idle
I have a 1998 F150 with a few problems. First one that is most annoying is the intermittent idle i have. It is not always rough, but out of the blue it will get rough idle and stay that way for awhile. Now I have already changed the following: Fuel filter, fuel pump, coil pack, spark plugs, spark plug wires, egr valve, iac valve, checked for vacuum leaks. The only codes I have ever gotten are for misfires on cylinder 6 and 1 at different times. Some times very rarely the truck wont start on the first try and it will start on the second go. I have cleaned the MAF sensor also. I am almost out of ideas on this problem.
The other issue is it sounds like a knocking lifter. I plan to replace all the lifters in the near future. This wouldnt cause the intermittent idle would it?
Thanks for any help you can give me.
The other issue is it sounds like a knocking lifter. I plan to replace all the lifters in the near future. This wouldnt cause the intermittent idle would it?
Thanks for any help you can give me.
Postmaster
Joined: Aug 2001
Posts: 4,532
Likes: 5
From: Trussville, Alabama
Sounds like you have already hit my first suspicions: Vacuum line or IAC.
I can't say that I'd suspect a bad lifter to cause erratic idle like you describe, but maybe so
I'd try resetting the ECU. Disconnect the battery, turn the headlights on, and let it sit for a few minutes.
Then reconnect the battery and start it up and let the ECU relearn.
Might help. Worth a try!
I can't say that I'd suspect a bad lifter to cause erratic idle like you describe, but maybe so
I'd try resetting the ECU. Disconnect the battery, turn the headlights on, and let it sit for a few minutes.
Then reconnect the battery and start it up and let the ECU relearn.
Might help. Worth a try!
New User
Joined: May 2011
Posts: 12
Likes: 0
Erratic Idle
Are you loosing coolant??? Or is dissapearing??? I have the same simptom with a bunch of codes and missfires all over. Of course the lower manifold gasket is bad but when I remove the plenum, found the IAC vaccum tube connection under the plenum, was busted. This may be your only trouble. Usually will give you codes 0171 and 0172 if is a vaccum related trouble. Hope you dont have an issue with the lower manifold gasket as it is a known problem with the 4.2 engine! My 2 cents!
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