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Has anyone experienced a misfire at idle but no engine light turned on? Also nothing comes up on scanner for stored codes.
I filled up gas on Tuesday night, Wednesday morning took the car to work and it started misfiring at the light and would stop by 1500-2000 rpm, then it completely went away. Next day nothing happened and then today on the way to work it happened again. I purchased new plugs and going to see if that resolves it, the car does have a stage 2 DME tune with intake and DP.
Would anyone have any idea what this may be? Could it be just bad fuel?
If you just filled up gas the night before, then bad gas would be my first thought as well. No such things as a coincidence as they say. As for the CEL, as far as I know it takes a certain number of consistent and significant misfires before it gets logged and the CEL lights up. But once the engine is tuned, everything kinda goes out the window. Who knows what the tune potentially messes up.
If you just filled up gas the night before, then bad gas would be my first thought as well. No such things as a coincidence as they say. As for the CEL, as far as I know it takes a certain number of consistent and significant misfires before it gets logged and the CEL lights up. But once the engine is tuned, everything kinda goes out the window. Who knows what the tune potentially messes up.
took it in the shop today, CEL finally popped up yesterday. We replaced the spark plugs and started it up, same issue kept happening. I drove it to the gas station and put fresh 93, started it up and no longer had rough idle. Parked it at the shop and left it idling for 30 minutes with no issue. Figured it was all good now, drove 15 miles home and as soon as I got home it happened again.
I attached a photo of the codes below, I think my next step is using the tuner handheld to upload the original stock file and seeing if that changes anything.
Did a few quick Google searches on those codes, and I found several posts with similar codes saying it's commonly caused by worn out exhaust valves seats causing leaking in the affected cylinders. Fix is a new cylinder head. Here's an example.
Different engine, but some of the same codes. Some other off the cuff ideas are failing injectors or fuel pump. Lean conditions basically mean not enough fuel is making it into the combustion chamber, so that could mean air is measured improperly and too much air is getting in, or not enough fuel or it's leaking out somewhere. I haven't seen this on the M177 engine TBH. Misfires on our engines are usually coils or fouled spark plugs in tuned cars, but then again, anything can go wrong in a tuned car that shouldn't under normal operation conditions.
Last edited by superswiss; Jun 14, 2025 at 01:25 PM.
Did a few quick Google searches on those codes, and I found several posts with similar codes saying it's commonly caused by worn out exhaust valves seats causing leaking in the affected cylinders. Fix is a new cylinder head. Here's an example.
Different engine, but some of the same codes. Some other off the cuff ideas are failing injectors or fuel pump. Lean conditions basically mean not enough fuel is making it into the combustion chamber, so that could mean air is measured improperly and too much air is getting in, or not enough fuel or it's leaking out somewhere. I haven't seen this on the M177 engine TBH. Misfires on our engines are usually coils or fouled spark plugs in tuned cars, but then again, anything can go wrong in a tuned car that shouldn't under normal operation conditions.
yeah I had seen that same post, it’s just that it’s complete different motors. Like what you said, I haven’t heard of anything like this on m177. Also wouldn’t worn out valve cause it to give persistent issue? Mine has been coming and going, I would hope it’s just injectors needing to be replaced.
yeah I had seen that same post, it’s just that it’s complete different motors. Like what you said, I haven’t heard of anything like this on m177. Also wouldn’t worn out valve cause it to give persistent issue? Mine has been coming and going, I would hope it’s just injectors needing to be replaced.
I guess it depends. If they are just slowly starting to leak then it could be intermittent. Metal expands and such. Might wanna do a compression test.
I guess it depends. If they are just slowly starting to leak then it could be intermittent. Metal expands and such. Might wanna do a compression test.
So far what I’ve done was replace plugs, replaced cyl 1-4 with new injectors which were also coded, flipped around coil packs and flipping around o2 censors, aswell as did a compression test which the results were excellent but all still showing Self-adjustment in idle speed range, right cylinder bank
Actual value : 6.52%
Specified value: [-4.50 - 4.50]
The car is tuned so I tried switching to the stock file, which made it completely worse. Threw misfire codes on cyl 3,4 and 5.
So decided to put back the tune file, car vibrates hard on idle and I know that the issue is the right side of engine. When putting it in Drive or Reverse the misfire/hesitation gets terrible. But in P or N , car is reacts different.
I’ve attached what xentry has shown, it would be amazing if anyone has any experience or sharing your thoughts. I’m really upset about this and bummed out I can figure it out.
The engine vibrations and misfires are a catch-22: one causes the other.
-- What are your idle LTFT ?
-- What are your compression individual numbers ??
You know these ECU are super precise. They quickly pull back fuel on individual cylinders or hand it out when satisfied by combustions.
The best outcome is with all cyl nearly equal.
You'll want to help your engine run predictably to meet ECU expectations else it enforces fuel penalties resulting in lean misfires.
Last edited by CaliBenzDriver; Jun 21, 2025 at 07:34 PM.
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