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upmaine
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Jan 30, 2012, 8:30 PM
Post #1 of 6
(5794 views)
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Idling at 1200 rpm.
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1995 Chevy Cheyenne 1500 with 350 engine. About a week ago I noticed that the idling was high. Usually it would idle around 700/800 and now it's idling right at 1200. It doesn't go up or down or fluctuate at all. it stays right at 1200. When I put it into gear the idle drops down to around 800 but I can feel the truck wanting to take off on it's own. So when I am driving if I take my foot off gas pedal the truck will stay going around 25 mph all by itself. As soon as I put it into park or neutral the rpm goes right up to 1200 instantly and it stays at 1200 until I put it into gear. Does anyone have any ideas as to what can be causing this. Kevin
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Discretesignals
Ultimate Carjunky
/ Moderator
Jan 30, 2012, 8:59 PM
Post #2 of 6
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Re: Idling at 1200 rpm.
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Take the air cleaner off and look at the top of the throttle body. Where the IAC motor is on top there is a little triangular hole next to one of the mounting bolts. With the engine running and idling high cover the hole and see if the engine stalls out. If it doesn't stall, you have a large vacuum leak. Pay attention to the throttle body gasket. They are known for getting sucked into the intake. If you open the throttle and look down inside the bore, you may even see a piece of the gasket hanging inside.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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upmaine
User
Feb 1, 2012, 12:45 AM
Post #3 of 6
(5730 views)
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Re: Idling at 1200 rpm.
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I covered the hole really good in the throttle body and the engine stalled. I tried it several times and each time the engine stalled. Do you have any more suggestion that i can try.
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Discretesignals
Ultimate Carjunky
/ Moderator
Feb 1, 2012, 5:59 AM
Post #4 of 6
(5721 views)
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Re: Idling at 1200 rpm.
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They make a little IAC driver tester with red and green lights that plugs into the connector for the IAC. When you turn the key on, you should see the lights on the tester flashing.
If your getting command from the ECM to the IAC motor, more than likely the IAC motor is bad. You can also ohm out the stepper coils in the motor to see if you have an open. Compare the readings you get from a known good motor. If you end up removing the IAC motor, clean the pintle bore with carb cleaner and a bottle brush.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Feb 1, 2012, 6:00 AM)
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theFreeMechanic
New User
Feb 4, 2012, 5:07 PM
Post #5 of 6
(5680 views)
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Re: Idling at 1200 rpm.
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Check for a seized or over-tightened throttle cable, they'll commonly fail due to high heat or just wearing out.
There should be a reasonable amount of slack in the cable, and it's usually adjusted very easily with a couple of wrenches.
A seized cable can work temporarily by lubricating the inside of the liner, but I strongly recommend replacing it with a new cable.
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(This post was edited by Discretesignals on Feb 4, 2012, 5:23 PM)
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Discretesignals
Ultimate Carjunky
/ Moderator
Feb 4, 2012, 5:20 PM
Post #6 of 6
(5673 views)
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Re: Idling at 1200 rpm.
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If the cable was seized and keeping the throttle blade open, the engine wouldn't have stalled when the intake hole for the IAC was covered.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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