Inconsistent misfiring in idle/drive/reverse below 1500rpm - no engine lights
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Joined: Apr 2022
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From: Gold Coast, Australia
C63 AMG P31
Inconsistent misfiring in idle/drive/reverse below 1500rpm - no engine lights
Hi everyone,
I am a bit puzzled by a recent issue that has come to light following the replacement of my spark plugs, ignition coils, and an intake cam adjuster.
I had the parts replaced to deal with severe misfiring and the car now drives well, save for the revs fluctuating by up to 200 rpm when idling, or accelerating/reversing which can be felt in the cabin (likely misfire). However, the fluctuations are not consistent in timing. There are no engine lights on the dashboard when it happens.
For some preface into symptoms/current diagnosis:
When I took the car out later in the day, I did have two singular misfires (within the same rpm range). Idle misfires were not apparent. Then, when I parked my car, I was in reverse gear and with my foot on the brake and the car was misfiring consistently without throwing a code. When I put the car into park, the misfires stopped.
I have done some looking online and through the forums and have identified the following potential issues:
Thanks everyone!
I am a bit puzzled by a recent issue that has come to light following the replacement of my spark plugs, ignition coils, and an intake cam adjuster.
I had the parts replaced to deal with severe misfiring and the car now drives well, save for the revs fluctuating by up to 200 rpm when idling, or accelerating/reversing which can be felt in the cabin (likely misfire). However, the fluctuations are not consistent in timing. There are no engine lights on the dashboard when it happens.
For some preface into symptoms/current diagnosis:
- The fluctuations only seem to appear below 1500ish rpm. Example, when accelerating slowly I would feel two to four misfires until the revs went above 1500ish rpm
- The car has returned a P0030 misfire in cylinder 3 code which appears and disappears at random - sometimes it does not even appear. No other codes are thrown such as a "lean" or "rich" fuel code.
- For about 3 weeks before the repairs, the car sat under a tree due to severe misfiring now fixed with new sparkplugs and ignition coils, and our initial thoughts have been to clean out the MAF sensors and the air intake filters which has not helped.
- The MAF sensors have been tested and appear to be running fine.
- The car otherwise drives fine.
When I took the car out later in the day, I did have two singular misfires (within the same rpm range). Idle misfires were not apparent. Then, when I parked my car, I was in reverse gear and with my foot on the brake and the car was misfiring consistently without throwing a code. When I put the car into park, the misfires stopped.
I have done some looking online and through the forums and have identified the following potential issues:
- Vacuum leak
- MAF sensors
- Air filters
- O2 Sensor
- Fuel injectors
- Fuel rail pressure
- PCV valve
- Air Conrol value
- Carbon buildup
- Spark plug seating/gap
- Timing
- Throttle position sensor
- Throttle body
- Clogged EGR valve
Thanks everyone!
