Rough idling and engine misfire?

Tiny
KAOMA
  • MEMBER
  • 2002 MAZDA 6
  • 2.0L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 254,709 MILES
Hi All,

For the past 2 years, I have had a rough idle and engine misfire. The cars always has a rough idle when idling, it gets worse when I engage the gear (drive or reverse), and when I turn on the A/C, when I press the gas pedal to raise the revs the rough idle disappears and runs smooth with high revs, and drives just fine when driving in high way or normal driving, when I stop at a red right it idles rough and at times can even switch off. The other problem is engine misfire, this does not happen all the times, but happens sometimes, basically you can have the engine misfire today as you start it up or even stop at a stop sign or red right, then the engine can run without misfiring for days then misfired again.

The things I have changed, throttle body, spark plugs, fuel pump and fuel filter, fuel injectors, coil pack, high tension cables, EGR valve, battery, Alternator, MAF sensor, Oxygen sensor, coolant temperature sensor, A/C compressor, Steering pump. I have tried disconnecting the battery, then reconnecting it and leaving the vehicle idling for 30 minutes, then turning on accessories and leaving it running for another 30 minutes, but this has not helped at all.

Please, what really could be the problem, I am really tired of spending money on the repairs to the point I just parking it. It is an LF engine.
Thursday, April 4th, 2024 AT 8:42 AM

10 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,665 POSTS
Hello,

I will help you fix the problem; can I ask if the check engine light is on? Also, I have seen a bad fuel injector cause this problem. Here is a guide to help you run the codes and we should do a compression test to make sure the engine is in good shape.

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

and

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

When you remove the spark plugs look for the one that is a different color than the rest, this will be the cylinder having an issue. If you upload a short video of the engine cranking over, I can tell if the engine is hurt or not. Please go over these guides and get back to us.

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Friday, April 5th, 2024 AT 9:22 AM
Tiny
KAOMA
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Hi Ken, I am so sorry for the late response, for the past weeks I was in an area with limited internet connection. I have inquired around for a garage with a compression gauge, I have not found one yet, but I am still looking around. I will upload a photo of the spark plugs and then upload the video of the engine cracking later in the day.
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Thursday, May 2nd, 2024 AT 3:15 AM
Tiny
KEN L
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Sounds good, have you tried Amazon? A compression gauge set starts at $14.00. I await your videos and results.
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Thursday, May 2nd, 2024 AT 12:56 PM
Tiny
KAOMA
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This is a video on cold start.
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Monday, May 13th, 2024 AT 10:31 AM
Tiny
KAOMA
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Spark plug 1.
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Monday, May 13th, 2024 AT 10:38 AM
Tiny
KAOMA
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Spark plug
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Monday, May 13th, 2024 AT 10:42 AM
Tiny
KAOMA
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I got new spark plugs today, the misfiring has improved but still have a rough idle. I have not been able to locate a garage with the compression gauge. Is there a way to test the compression without the gauge?
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Monday, May 13th, 2024 AT 10:45 AM
Tiny
KEN L
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Not really, thanks for the video, I can hear some engine noise I don't like, it sounds like you may have a roller follower or a flat camshaft, I would do the compression test first because in the video it looks like you may have one cylinder that is low on compression.
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Tuesday, May 14th, 2024 AT 9:34 AM
Tiny
KAOMA
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Thank you Ken, I will keep looking, hope I come across someone with a compression gauge soon. I will keep you updated.
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Tuesday, May 14th, 2024 AT 10:25 AM
Tiny
KEN L
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Sounds good.
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Wednesday, May 15th, 2024 AT 9:39 AM

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