Low/rough idle

Tiny
STARLORD1976
  • MEMBER
  • 2008 CHEVROLET IMPALA
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 150,000 MILES
When in park car will keep hesitating like it wants to shut off sometimes.
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Wednesday, March 16th, 2022 AT 7:04 AM

7 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

The most common cause of a low or rough idle is an engine vacuum leak. That is where I would start checking.

Here is a link that explains how it's done:

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

If this is something you have already done or it yields no repair, then we need to check if there are diagnostic trouble codes, if there is an issue with fuel pressure, or if the idle air control valve is going bad or simply needs to be serviced.

The idle air control valve (IAC) is responsible for maintaining engine idle speed. If it fails, oftentimes the idle speed will fluctuate up and down, or stalling can occur.

Let me know if you are able to perform the vacuum test.

I will watch for your reply.

Take care,

Joe
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Wednesday, March 16th, 2022 AT 4:35 PM
Tiny
STARLORD1976
  • MEMBER
No codes, no leaks, and I’m not sure if my car has IAC. Valve?
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Saturday, April 2nd, 2022 AT 1:22 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

I did a little research, and although the manual has specifications for an IAC, it doesn't show one. So, you may be correct.

If there are no engine vacuum leaks, I looked for an idle speed relearn procedure. I found it. There is one with a scan tool and one without. To add insult to injury, the one for doing without a scanner tells you to watch the scan tool. LOL

However, I don't feel the scan tool does anything but show the RPM speed. Do me a favor. Take a look through the attachments and see if they help change the speed.

I will watch for your reply.

Take care,

Joe
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Saturday, April 2nd, 2022 AT 9:06 PM
Tiny
STARLORD1976
  • MEMBER
Tried it twice still didn’t help.
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Monday, April 4th, 2022 AT 12:20 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

By chance, have you had a chance to check for vacuum leaks? Also, have you ever serviced the throttle body?

Here is a link that explains in general how it is done. Try this as well.

https://www.2carpros.com/articles/throttle-actuator-service

Let me know if you checked for vacuum leaks. Also, I need to confirm if this is the 3.5L or the 3.9L V6.

Let me know.

Joe
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Monday, April 4th, 2022 AT 6:27 PM
Tiny
STARLORD1976
  • MEMBER
3.5, I checked the vacuum best I know how never did it before. I had throttle body cleaned out. And I had plugs changed and they said that the plugs were running lean.
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Tuesday, April 5th, 2022 AT 8:27 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

If it is running lean, either it is a vacuum leak issue or low fuel pressure. If you found no leaks, the next thing to check is fuel pressure to make sure it isn't low.

Here is a link that explains in general how it's done:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

I attached the manufacturer's fuel pressure specifications below.

Let me know what you find.

Joe
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Tuesday, April 5th, 2022 AT 5:49 PM

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