Rough idle?

Tiny
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.
Tuesday, January 23rd, 2024 AT 9:29 PM

3 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 51,685 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

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
Tiny
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
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 51,685 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.
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Monday, January 29th, 2024 AT 9:31 AM

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