what causes an engine to idle high?
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From: Waterloo ontario Canada
Re: what causes an engine to idle high? (daniel77350)
The motor is getting air from someplace. If the chock is stuck on it will be very rich and a quick look under the air cleaner will confirm this. The idle speed screw could be also to high, the fast idle screw on the choke side, the throttles not returning to fully closed or a missing vacuum line, leak from headlight assembly. If you can't find anything how about pinching some of the vacuum lines off to see if that is a source of air. It is comming form someplace. Even the vacuum brake booster.
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Re: what causes an engine to idle high? (daniel77350)
Daniel, A few things can cause this. One is a bad choke pull-off that is not opening up your choke all the way once your car is warmed up and another is there is a "fast idle" step cam on the passenger side of the carb. When the car is cold, and the choke sets this "fast idle" cam for cold fast idle, it can remain in the fast idle position if it is "gummy". You can use WD-40 or carb cleaner on it to loosen it up. It is like a little pendulum weighted lever, but like I said, if it's dirty and gummy, it won't let your throttle on your carb "idle-down".
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Drifting
Joined: Aug 2001
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From: North Carolina
Re: what causes an engine to idle high? (Tom454)
its a rochester(sp?)
anyway, the carb has two seals on it. One near the top and one near the bottom. The bottom one was wet from fuel, so I removed the carb and tightened the bottom screws just a hair. When I put the carb back on she fired right up and didn't idle very high at all. So I took it for a little spin and it performed good. My tires are a little underinflated though...whats a good PSI to make them?
Daniel
anyway, the carb has two seals on it. One near the top and one near the bottom. The bottom one was wet from fuel, so I removed the carb and tightened the bottom screws just a hair. When I put the carb back on she fired right up and didn't idle very high at all. So I took it for a little spin and it performed good. My tires are a little underinflated though...whats a good PSI to make them?
Daniel
Drifting
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From: Schaumburg IL
Re: what causes an engine to idle high? (daniel77350)
Looks line most common causes have been covered. Take a look with a flashlight and make the secondaries are closed. Push on them with a long screw driver to make sure they are closed. Varnish could be holding them open a tad bit and that's an air leak. Sometimes these are tough problems.
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From: honolulu HI
Re: what causes an engine to idle high? (daniel77350)
i had the same problem untill the other day when i asked lars for help..he said to turn the idle screw facinging forward on the front right side of carb.. did this and the idle is nice and mellow now :)
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Drifting
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From: North Carolina
Re: what causes an engine to idle high? (razz1980)
idle screw is as low as it can get. Im messing with the fuel/air screws but those don't seem to do much. Im sure my carb is gummed up with something...A new carb is on my list of "to-do's before college"
Daniel
Daniel
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Drifting
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From: North Carolina
Re: what causes an engine to idle high? (Paul 75 L82)
ok, the high idle came back this afternoon. It was accompanied by run-on. (after I shut the car off, it studders for a second then finally dies).
I wish I could tell you how high the idle is, but my tach is bad. If I had to guess, the high idle would be around 2-3K
Daniel
I wish I could tell you how high the idle is, but my tach is bad. If I had to guess, the high idle would be around 2-3K
Daniel
Drifting
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From: Kirkland WA
Re: what causes an engine to idle high? (razz1980)
This sounds almost 100% like a choke pulloff/fast idle problem.
The car is going to diesel when you shut it off at 2K rpms. Had this same problem in my old Mustang and it was because the fast idle cam would sometime re-engage when I hit the throttle. Idle would shoot up and it would surge on shutdown.
Take the carb off the car, get yourself a good rebuild kit, a bunch of carb cleaner and work through the carb. Get Lars' tuning paper. You can get the carb apart, cleaned and rebuild in one evening even if it's your 1st time.
I'm sure you'll find a linkage that is stuck/binding/etc. once you work through all the mechanicals.
Also, turn down your fast idle screw. Adjusting your normal idle won't do anything if the fast idle is engaged. That should at least prevent you from runnig up the RPM's, but it will make cold starting harder.
Good luck!
The car is going to diesel when you shut it off at 2K rpms. Had this same problem in my old Mustang and it was because the fast idle cam would sometime re-engage when I hit the throttle. Idle would shoot up and it would surge on shutdown.
Take the carb off the car, get yourself a good rebuild kit, a bunch of carb cleaner and work through the carb. Get Lars' tuning paper. You can get the carb apart, cleaned and rebuild in one evening even if it's your 1st time.
I'm sure you'll find a linkage that is stuck/binding/etc. once you work through all the mechanicals.
Also, turn down your fast idle screw. Adjusting your normal idle won't do anything if the fast idle is engaged. That should at least prevent you from runnig up the RPM's, but it will make cold starting harder.
Good luck!
