High Idle topic (again!)
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Cross-Country
Joined: Jan 2015
Posts: 80
Likes: 5
High Idle topic (again!)
Hey guy's, I've tested and replaced alot of switches on my 1991 5.8 and its running really well thanks to the advise of some of you guy's. But, at times I still have the dreaded high idle issues, not all the time but it will be idling fine and then change. Last week I tapped on the MAP sensor and it idled down! On the next high idle I did it again! and idled down. It doesnt repeat everytime but sometimes it works.
I attemped to test it but didnt seem to have much luck with that. So I was wondering, could the MAP sensor cause the occasional high idle? thanks
I attemped to test it but didnt seem to have much luck with that. So I was wondering, could the MAP sensor cause the occasional high idle? thanks
Thread Starter
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Cross-Country
Joined: Jan 2015
Posts: 80
Likes: 5
Yes, I agree with you on that. But this is different. It can be idling high and for not apparent reason idle down like it should. Almost like it's getting a signal to do so. Come to a stop after driving and it can be high idle, sometime I can tap the throttle and it will idle down. Other times I can switch it off and restart and its correct. So it's not a constant part malfunction. I've set the voltage on the TPS, cleaned the IAC, no Vaccum leaks. Just thinking what part could make this act this way. thanks
Fleet Owner
Joined: Oct 2005
Posts: 20,783
Likes: 1,751
From: Kentucky
Yes, a MAP sensor can cause a high idle. Simply tapping it may mean there is a small crack allowing a vacuum leak to occur or electrically it could have a crack in the internal electronics. It could also be a simple bad electrical connection to the MAP.
How were you testing it before?
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How were you testing it before?
.
Senior User
Joined: May 2015
Posts: 466
Likes: 2
From: Dallas, TX
Others will dislike me for this suggesting replacement before troubleshooting. - Just replace it and see. Its two bolts and its like a $10 part at the auto store. I thought about testing with a meter but once I knew it was a cheap replacement I did it just to move onto the next possible solution. I bought one; replaced it and my truck ran better but was not ultimate cause of my issue(s). I still have the OEM one to go back to if I feel the need but have not yet and too late to return the newer one.
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Senior User
Joined: May 2015
Posts: 466
Likes: 2
From: Dallas, TX
Also if your looking for vacuum leaks. I'd start with the metal can if yours is pre 94 and not the plastic one and just go ahead and replace all the plastic vacuum lines (would not be surprised if one is cracked) with rubber or silicone lines. Of course throw a gauge on it first!
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