Rough idle?

ROADMONGER

MEMBER
1997 BMW Z3
1.9L
4 CYL
2WD
AUTOMATIC
94,500 MILES

The idle is very rough. I have no check engine lights. The latest diagnostic test did not show an error code. I have new vacuum hoses. The car has been tested for air leaks and there are none. Fuel mileage is normal. Acceleration is normal. Shifting is normal. In the past six months the car has been examined thoroughly at two auto shops that specialize in older cars/imports. I am at a loss. I can't find the problem.

3 Replies

KEN L

MASTER CERTIFIED MECHANIC
42,949 POSTS

Anytime you have a rough idle with no vacuum leaks it is best to do a compression test. Also, while the spark plugs are out let's compare the color on each. Please upload any images of the spark plug so I can see them.

Here are two guides to help us see what's going on:

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

and

https://www.2carpros.com/articles/troubleshooting-rough-idle-in-your-cars-engine-7-common-causes-and-how

Please upload pictures or videos in your response to the problem so we can see what's going on.

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Wednesday, January 24th, 2024 AT 11:18 AM

ROADMONGER

MEMBER
1 POST

I recently installed new plugs and coil packs. The compression was checked at that time.

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Sunday, January 28th, 2024 AT 12:02 PM

KEN L

MASTER CERTIFIED MECHANIC
42,949 POSTS

What were the readings please? Also, can you please upload a short video of the engine idling so I can see it? It sounds like the fuel injectors may need replacement, here is a guide to help you test them to confirm the failure.

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

Does the engine make any unusual noises at idle? Check out the images (below). Please let us know what happens.

Images (Click to make bigger)