funny fast idle
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Joined: Dec 2008
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funny fast idle
Hi all,
I have a 1991 5.7 TBI motor in my 1987 Land Cruiser and have an odd intermittent fast idle problem. When stone cold, the truck will not idle below 1000 rpm's when hot. This occurs only when started stone cold the 1st time. Any starts after that the truck idles correctly around 700 rpm's. I can run around all day start/stop and as long as I have started it after it has heated up all is good.
However, if I let it cool to stone cold, the 1st time I start it it is back to the 1000 rpm's after warmed up. It is as though a restart clears the problem when warmed.
No codes present.
Any ideas?
Don
I have a 1991 5.7 TBI motor in my 1987 Land Cruiser and have an odd intermittent fast idle problem. When stone cold, the truck will not idle below 1000 rpm's when hot. This occurs only when started stone cold the 1st time. Any starts after that the truck idles correctly around 700 rpm's. I can run around all day start/stop and as long as I have started it after it has heated up all is good.
However, if I let it cool to stone cold, the 1st time I start it it is back to the 1000 rpm's after warmed up. It is as though a restart clears the problem when warmed.
No codes present.
Any ideas?
Don
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From: Moorestown, NJ
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
Re: funny fast idle
Welcome to TGO!
Several things come to mind. First would be worn throttle blades. These can cause the throttle to hang open sometimes, resulting in a fast idle.
Second would be a faulty IAC thats dirty, and can no longer move properly. This is especially true if the IAC is original and has a lot of deposits on it. Replacements can be had for around $35 or so from most autoparts stores.
Last thing could be a vacuum leak or a leaking vacuum accessory thats allowing the motor to take in more air then it should.
There are other possibilities, but check these first and see what you find.
Several things come to mind. First would be worn throttle blades. These can cause the throttle to hang open sometimes, resulting in a fast idle.
Second would be a faulty IAC thats dirty, and can no longer move properly. This is especially true if the IAC is original and has a lot of deposits on it. Replacements can be had for around $35 or so from most autoparts stores.
Last thing could be a vacuum leak or a leaking vacuum accessory thats allowing the motor to take in more air then it should.
There are other possibilities, but check these first and see what you find.
Thread Starter
Junior Member
Joined: Dec 2008
Posts: 2
Likes: 0
Re: funny fast idle
Thanks for the response Dimented. See below for my thoughts.
Welcome to TGO!
Several things come to mind. First would be worn throttle blades. These can cause the throttle to hang open sometimes, resulting in a fast idle.
(recent rebuild form Turbo City on the throttle body so I'm guessing that was probably checked. Also, if I do a cold start, let run till hot, turn off, re-start without touching throttle it idles down properly)
Second would be a faulty IAC thats dirty, and can no longer move properly. This is especially true if the IAC is original and has a lot of deposits on it. Replacements can be had for around $35 or so from most autoparts stores.
(recent rebuild on TB so no deposits on IAC as I checked. The new IAC that is in it can be bad I suppose even though new)
Last thing could be a vacuum leak or a leaking vacuum accessory thats allowing the motor to take in more air then it should.
(checked seven ways till Sunday. Pretty sure none present)
There are other possibilities, but check these first and see what you find.
Several things come to mind. First would be worn throttle blades. These can cause the throttle to hang open sometimes, resulting in a fast idle.
(recent rebuild form Turbo City on the throttle body so I'm guessing that was probably checked. Also, if I do a cold start, let run till hot, turn off, re-start without touching throttle it idles down properly)
Second would be a faulty IAC thats dirty, and can no longer move properly. This is especially true if the IAC is original and has a lot of deposits on it. Replacements can be had for around $35 or so from most autoparts stores.
(recent rebuild on TB so no deposits on IAC as I checked. The new IAC that is in it can be bad I suppose even though new)
Last thing could be a vacuum leak or a leaking vacuum accessory thats allowing the motor to take in more air then it should.
(checked seven ways till Sunday. Pretty sure none present)
There are other possibilities, but check these first and see what you find.
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