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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.
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Thursday, April 4th, 2024 AT 8:42 AM

21 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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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
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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
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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
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Spark plug
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Monday, May 13th, 2024 AT 10:42 AM
Tiny
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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
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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
Tiny
KAOMA
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Hi Ken, I know it's been a ages, I had parked the car and was almost never using it, to cut the story short, I managed to spend time to open the engine and found one of the valve was broken on the edge, I replace the valve, as well as the valve seals and piston rings as it used to burn oil.

After assembling it, it started and ran just fine for a few days. Now I it has started having a rough idle and misfires sometimes, it is also hesitating when accelerating and jerks a lot when driving between 60 - 80 kilometers. This gets worse when the A/C is on.

Please note that the rough idles does not happen all the time, sometimes the car idles fine without misfiring or rough idles, and sometimes it accelerates just fine, but it always jerks when I start driving it between 60 - 80 kilometers.

I did replace the spark plugs the same time I opened the engine. I just replaced the fuel pump, but it does not seem to solve the problem, and if you refer back to my initial question at the top, you will see I had changed almost any other sensor before.

Please note it does not have the engine check light on and does not bring any codes when scanned.

I post so you see what I am talking about.

Thank,
Kaoma.
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Wednesday, December 4th, 2024 AT 11:36 PM
Tiny
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Below is a video of the car running smooth without misfiring or rough idle.
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Wednesday, December 4th, 2024 AT 11:55 PM
Tiny
KEN L
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Yes, that does idle well. Thanks for the video. I have seen a cracked spark plug or a bad ignition coil cause this, I would remove the spark plugs to check for cracks and replace the ignition coils. I would replace the spark plug wires as well. Check out the images (below). Please let us know what happens.
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Thursday, December 5th, 2024 AT 1:21 PM
Tiny
KAOMA
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Hi Ken,

This morning I decided to try something (not recommended), I took out the pump and bypassed the fuel filter, you are not going to believe I never suspected the fuel filter since I change it middle last month. After bypassing the fuel filter, it did idle quiet well, I tried driving it and it did not jerk when I got to drive it between 60 - 80km, and there was no hesitation during acceleration. I tried to turn on the AC and the engine still ran quiet well. I believe I found my problem. I will be getting a new fuel filter after work, I will also clean the fuel injectors as I install the filter.

I really hope this is the solution and the problem will not come back.

Thank you,
Kaoma
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Friday, December 6th, 2024 AT 12:04 AM
Tiny
KEN L
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You must have gotten a bad tank of gas which can clog the fuel filter. Good find. Please upload an image of the filter so I can see.
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Friday, December 6th, 2024 AT 9:46 AM
Tiny
KAOMA
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Hi Ken, I gave it some days to observe the car as I waited to buy the filter, I have not gotten the filter yet as prices have sky rocketed the past months due to inflation in my country. The problem came back after 2 to 3 days or driving it without a fuel filter, so now I am not sure if it is the filter. So here is how it is behaving, when it has been parked for a long time, I start it, and it starts with misfiring, when you drive it, it misfires, you press the gas pedal it does not accelerate, then just kicks in after keeping the foot on the gases, then loses power, then kicks in again, then loses power, keeps doing this until it picks up speed, it never goes off. As you keep moving it begins to improve, after driving it for some time, the misfiring goes away and it drives normal, accelerates normal, you can turn off the engine when you get to a shopping mall, and when you are back from the store, it starts right up without any misfiring, and drives super normal, accelerates super normal.

Honestly, I feel like giving up on the car.

Thank you,
Kaoma
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Monday, December 16th, 2024 AT 9:55 AM
Tiny
KEN L
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Are there any trouble codes? Also, those spark plugs like the engine is running rich like it has a clogged catalytic converter. If you use a rubber mallet on the exhaust, can you hear something rattling inside?
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Tuesday, December 17th, 2024 AT 10:15 AM
Tiny
KAOMA
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Hi Ken,

I do not have a rubber mallet, but sometimes I hear rattling noise as the engine runs. And there are no codes, no lights on the dashboard, the spark plugs are new, I got them last month. Is it possible to clean the catalytic converter?
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Tuesday, December 17th, 2024 AT 10:22 AM
Tiny
KEN L
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Not if it is broken inside, which is common. You might be able to remove it and see if you can get the broken pieces out to see if it helps the engine run better, that way you will know for sure if that is the problem.
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Tuesday, December 17th, 2024 AT 10:28 AM
Tiny
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Hi Ken, thank you. I will do that over the weekend, I will give you an update.

Thank you
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Tuesday, December 17th, 2024 AT 10:53 PM

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