Idle problems
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6th Gear
Joined: Jan 2024
Posts: 6
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From: Midwest
Idle problems
My 89 f-150 4.9 5 speed manual is surging from 800 to 1500 rpm, what could be causing this? Iac? Throttle position sensor? I have replaced both including new harness plugs. I took off throttle body and cleaned it out with throttle body cleaner and scrubbed the bores. Also on an unrelated note, when I am driving, and I shift... It cuts out for a split second, and when the throttle is pushed more it runs fine, just shifting it driving and hitting the acceleration, it also cuts for a brief second and goes back to normal, revving the engine in neutral it also does this floor it and it cuts for just a split second then catches up and reves freely. I assume throttle position or iac, but I replaced them ,I suppose I could have bad new parts? Any theories or tests or ideas? 💡 Thanks in advance!
Last edited by 89 4.9; Apr 13, 2025 at 08:04 PM.
FTE Legend
Joined: Nov 2015
Posts: 30,830
Likes: 4,094
From: Angier, NC
Being you have EFI and a computer I would pull codes and go from there.
But I am thinking you have a vacuum leak somewhere and it is making the IAC go bonkers and why it hunts.
Start spraying the intake and vacuum line with carb cleaner and when the RPM changes the leak is near by.
Dave ----
But I am thinking you have a vacuum leak somewhere and it is making the IAC go bonkers and why it hunts.
Start spraying the intake and vacuum line with carb cleaner and when the RPM changes the leak is near by.
Dave ----
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Mountain_anderson
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
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