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03-06-2024, 07:33 PM | #1 |
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Misfires and weird idle
Hi all,
I have a 2012 M3 6MT with ~57k. Since I bought it back in 9/2022, it’s had one issue, with another developing recently. 1) When warmed up and at idle, especially after driving for a while, the RPMs will suddenly drop and then bounce up/down for ~10-15s before either stabilizing or stalling (restart is fine). This doesn’t happen or worsen after refueling. No other patterns of note. 2) Back in October, I got a horrible miss followed by an engine malfunction/SES. Codes were for bank 2 O2 sensors, and misfires were for all bank 2 cylinders. The misfire cleared on the next restart, but now comes back intermittently after a hot start and lingers for a minute or two, then suddenly clears. Interestingly, it hasn’t re-triggered the SES/EM lights. For further context, when I got the car, it had high-flow cats/aftermarket O2 sensors/tune. Carvana ended up paying a *ton* to replace both cats, all four O2s and re-flash the car. The O2s have all been replaced a second time under warranty. I’ve also since replaced the spark plugs and moved coils around, both to no avail. Only codes that ever come back now are misfires. Anyone ever experience something similar? Either issue related, you think? Appreciate any insight! |
03-07-2024, 04:11 PM | #2 |
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Drives: E53 X5, E83 X3, E93 M3
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Get ISTA and run the ionic misfire detection. You could have a coil going out and moving them around is just going to continue them misfiring unless you know which ones you moved where and are tracking what you are doing.
P.S. You made sure to use the stock spark plugs, ya? This engine platform can only take one type of spark plug. Also, all the coils are OEM, ya? Please report back your findings.
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2008 BMW M3 E93 MT
R135 └┼┼┼ ..246 |
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03-07-2024, 11:21 PM | #3 |
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Thanks for the response!
* Plugs and coils are OE * Misfire hasnÂ’t followed the coils; itÂ’s static on the same bank every time Thinking IÂ’ll get it to a specialist of course, just hoping I might be able to gain some insight here if anyone else has been through it. The dealer tried pretty diligently a few times since I bought it in mid-2022, but canÂ’t replicate it and hasnÂ’t been able to diagnose it yet. Other thought is to just drive it until it completely dies or wonÂ’t come out of engine malfunction I guess. |
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03-08-2024, 12:08 PM | #4 | |
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Quote:
It'd be nice if you got some good readings of typical things during the issue. Like O2 readings/voltages...fuel trims LT/ST...fuel pressure... I bet there's a common issue here that just needs to be found. Some common ideas are the idle air control valve, fuel vent (maybe), SAI valves.... This is challenging to diag over the internet without substantial information/data.
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R135 └┼┼┼ ..246 |
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07-04-2024, 06:57 PM | #5 |
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Hello! my e92 m3 is having a rough idle and you can hear it misfire sometimes, when i go over 4k rpm it goes into limp mode and shuts the injector off on cyl 8, so i get a fault code 2b3c. i have changed the injectors, coils, spark plugs, had vaccum leak test, reprogrammed t dme, changed o2 sensors, checked throttle actuators, the air valve in the tank etc. i have no idea what to do next, i also had the cylinders inspected and compression tested no damage. What do i do next? the car only have 90k km on it. it only shows misfire on cyl 8 with cutoff.
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07-04-2024, 06:59 PM | #6 |
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Hello! my e92 m3 is having a rough idle and you can hear it misfire sometimes, when i go over 4k rpm it goes into limp mode and shuts the injector off on cyl 8, so i get a fault code 2b3c. i have changed the injectors, coils, spark plugs, had vaccum leak test, reprogrammed t dme, changed o2 sensors, checked throttle actuators, the air valve in the tank etc. i have no idea what to do next, i also had the cylinders inspected and compression tested no damage. What do i do next? the car only have 90k km on it. it only shows misfire on cyl 8 with cutoff.
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07-04-2024, 07:38 PM | #7 |
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Run the engine with the intake plenum removed. See if misfire goes away. If it does you may have a plenum leak.
Also check ground strap and exhaust header ring gaskets. |
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