High engine idle

Tiny
MROULET1
  • MEMBER
  • 1999 CADILLAC DEVILLE
  • 4.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 156,000 MILES
So my car have been having a really high idle. I changed out the position sensor and it it stopped for a little now it’s worse.
Tuesday, November 30th, 2021 AT 2:02 PM

5 Replies

Tiny
SQM
  • MECHANIC
  • 6,383 POSTS
Hello,

Are you getting any trouble codes? Is the check engine light illuminated?

One of the common reason for high idle is a faulty idle air control valve (IAC). Overtime dirt and debris can buildup inside the valve and cause it to stuck open, allowing more air than it supposed to. Which leads to a high idle.

The IAC can be serviced by cleaning it. Many times that improves the idle quality.

Take a look at this helpful guide:

https://www.2carpros.com/articles/engine-idles-too-high

I have attached diagrams for your reference.

Please let me know if you have any questions.
Thank you.

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Tuesday, November 30th, 2021 AT 2:39 PM
Tiny
MROULET1
  • MEMBER
  • 79 POSTS
So before changing I look to see if I had a code. Code po503 came up. Vehicle speed sensor A intermittent/Erratic/High. Is that the Idle air control?
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Thursday, December 2nd, 2021 AT 6:51 AM
Tiny
SQM
  • MECHANIC
  • 6,383 POSTS
The code P0503 is for the vehicle speed sensor circuit, not related to the idle air control valve. This usually gets triggered due to an issue with the speedometer or even shifting issues.

I have attached the trouble shooting guide for that code below for your reference.
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Thursday, December 2nd, 2021 AT 9:46 AM
Tiny
MROULET1
  • MEMBER
  • 79 POSTS
So, can that code be also why my car has that high idle?
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Thursday, December 2nd, 2021 AT 11:32 AM
Tiny
SQM
  • MECHANIC
  • 6,383 POSTS
It is a possibility. Go through that guide and see if it helps you determine the issue.
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Thursday, December 2nd, 2021 AT 9:37 PM

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