surging idle
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surging idle
Hello all,
I've been having a problem with my 89 f150 with the 4.9L straight 6. The problem is that it has a really bad surging idle when I first start the truck up, and it lasts for about 10 minutes or until the truck warms up. The RPM's will go from around 800-400. The colder it is outside, the worse it is.
After reading some forums, I thought maybe to replace my IAC. It made it worse. Now it runs for about 3 seconds and then stalls out, unless I have my foot on the gas. When I'm pressing the gas and taking it for a ride, it does seem to run better and maybe even with more power. When I let off the gas, it surges again. I turned it off and on a few times and it kept doing the same thing. I then took off the IAC and then put it back on and it idled at around 900 rpm's perfectly. I put the truck in gear, and the surging began again. The surging doesn't stop now unless my foot is on the gas pedal.
Any ideas?
It is not a vacuum leak either.
I've been having a problem with my 89 f150 with the 4.9L straight 6. The problem is that it has a really bad surging idle when I first start the truck up, and it lasts for about 10 minutes or until the truck warms up. The RPM's will go from around 800-400. The colder it is outside, the worse it is.
After reading some forums, I thought maybe to replace my IAC. It made it worse. Now it runs for about 3 seconds and then stalls out, unless I have my foot on the gas. When I'm pressing the gas and taking it for a ride, it does seem to run better and maybe even with more power. When I let off the gas, it surges again. I turned it off and on a few times and it kept doing the same thing. I then took off the IAC and then put it back on and it idled at around 900 rpm's perfectly. I put the truck in gear, and the surging began again. The surging doesn't stop now unless my foot is on the gas pedal.
Any ideas?
It is not a vacuum leak either.
Fleet Owner
Joined: Oct 2005
Posts: 20,780
Likes: 1,746
From: Kentucky
The most common causes of a rolling idle as you described are:
1.Vacuum leaks
2. Faulty IAC
3. Faulty TPS
4. Faulty Throttle Body
5. Sticking throttle cable.
Before changing any other parts try running the KOEO tests and stored code (aka Continuous Memory) display.
1.Vacuum leaks
2. Faulty IAC
3. Faulty TPS
4. Faulty Throttle Body
5. Sticking throttle cable.
Before changing any other parts try running the KOEO tests and stored code (aka Continuous Memory) display.
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