Rough idle?

MCLARK22

MEMBER
2005 CHEVROLET TRAILBLAZER
4.2L
6 CYL
4WD
AUTOMATIC
160,000 MILES

I am having a rough idle whether cold or hot, the engine bogs down when reversing and occasionally stalls, and there is a lack of accelerating power when A/C is running.

Thursday, August 10th, 2023 AT 4:13 PM

3 Replies

KEN L

MASTER CERTIFIED MECHANIC
48,323 POSTS

It sounds like you lost compression in one or more cylinders, do you have a check engine light on? If so, we need to run the codes to see what they are.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

If you can upload a short video of the engine running, I can tell what is wrong, or at least see what the next step should be. You may have a weak fuel pump as well. Here is a guide to help us test the fuel pressure.

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

Fuel Pressure (Key ON, Engine OFF) .................... 345-395 kpa (50-57 psi)

You can rent a fuel pressure gauge from the auto parts store. Please go over these guides and get back to us.

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Friday, August 11th, 2023 AT 10:40 AM

MCLARK22

MEMBER
2 POSTS

I don't have any current codes, but I have had 2 codes in the past. P0303 (misfire cylinder 3). That went away after a full plug and coil change. The plug in cylinder 3 did have oil on the electrode side. (Which I understand is usually indicative of advanced cylinder or piston wear. Just hoping there was something else it could be before I just decide to just drive the vehicle into the ground).
And P0495 (voltage reading that is too high from the electric cooling fan control circuit) which I cleared and it hasn't repeated.

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Friday, August 11th, 2023 AT 9:12 PM

KEN L

MASTER CERTIFIED MECHANIC
48,323 POSTS

If you have low compression on cylinder #3 this will account for the rough idle.

Here is a guide to help you confirm the issue:

https://www.2carpros.com/articles/how-to-test-engine-compression

Please go over this guide and get back to us.

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Saturday, August 12th, 2023 AT 10:08 AM