High idle

1999 CADILLAC DEVILLE
158,000 MILES
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MROULET1
  • MEMBER
  • 79 POSTS
I have a very high idle. I changed out the Idle air control valve with and the Throttle position sensor with aftermarket. It went away for a few days n came right back. It very hard to put in gear. It slams into gear when it’s doing it and feels like someone is passing the gas.
Dec 21, 2021 at 3:19 PM
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JACOBANDNICKOLAS
  • AUTOMOTIVE REPAIR CONTRIBUTOR
  • 110,190 POSTS
Hi,

By chance, have you had the computer scanned? I ask because there a few things that can cause the idle speed to increase. For example, the A/C system, Power Steering system, or anything that places a load on the engine at idle.

Also, engine vacuum leaks can also cause idle-related issues. How high does it idle when this happens and is there anything that you can think of that causes it or changes it?

Here is a link that explains how to test for a vacuum leak. Try this and let me know if you find anything.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Take care,

Joe
Dec 21, 2021 at 6:51 PM
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MROULET1
  • MEMBER
  • 79 POSTS
I have no vacuum leaks. It kind of just happens with or without any load. Every once in a while, I can start it and it will be good.
Dec 21, 2021 at 6:56 PM
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JACOBANDNICKOLAS
  • AUTOMOTIVE REPAIR CONTRIBUTOR
  • 110,190 POSTS
Hi,

Since the vehicle has a throttle cable, check to make sure it isn't frayed at any point, confirm it is properly attached at the pedal and throttle body, and make sure none of the mounts are loose.

Let me know what you find.

Take care,

Joe
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Dec 22, 2021 at 4:48 PM