High engine idle

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

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

MROULET1

MEMBER
76 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

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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