High idle

1999 CADILLAC DEVILLE
159,000 MILES • 4.6L • V8 • 2WD • AUTOMATIC
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MROULET1
  • MEMBER
  • 79 POSTS
When I start my car it idles anywhere between 1,500 to 2,000 RPMs all the time. I have changed MAF, IAC, TP, Intake. Every time I change a part it will run good for 4 days then back to the same high idle. I’m so stuck!
Jan 30, 2022 at 8:16 PM
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KASEKENNY
  • AUTOMOTIVE REPAIR CONTRIBUTOR
  • 18,907 POSTS
It is interesting that after you replace something that it works properly.

That tells me that we may have a PCM issue. Basically, after you replace the part, the PCM needs to "learn" the part and that may take some time. However, this is not 4 days so let's test this to see if this is a software issue or not.

Can you do a battery disconnect and touch the cables together to see if afterwards the idle is operating normally?

Also, here is a guide that will help with high idle issues, but I am not sure this will address yours due to its operating normally for a short time.

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

This shows that the parts are able to function normally but clearly the PCM is most likely causing the idle to go high due to adding more fuel.

Also, when you say you replaced TP, was this the throttle body assembly or did you replace just the sensor?

Let's start with this info and go from there.

Thanks
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Jan 31, 2022 at 6:05 PM
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