Misfiring On All Cylinders Only After Idling for a While

[sapote]

Car runs fine when I unplug the brand new MAF..

Something causing the bad mixture of fuel/air, and unplug the MAF forced the DME to use opened-loop control (ignore the O2 sensor signals) and so engine ran richer but smooth.

[lemoose]

id rule out the egt. Youre probably only seeing a code for it due to a lean condition- which points back to what sapote says above

[Halftim3]

Have you done a leakdown or compression test?A blown headgasket between the cylinders throws the same misfire CEL. It happens to some with lower mileage.

[giOsaurus rEx]

Something causing the bad mixture of fuel/air, and unplug the MAF forced the DME to use opened-loop control (ignore the O2 sensor signals) and so engine ran richer but smooth.

So sounds like the pre-cat O2s need to be replaced then? Or should both pre-cat and post-cat O2 sensors be replaced?

Have you done a leakdown or compression test?A blown headgasket between the cylinders throws the same misfire CEL. It happens to some with lower mileage.

No I haven't. I'm talking to the shop whose done a lot of work for me about this. It isn't throwing any lights on the dash, just codes when I scan with a ECS Tuning Foxwell scanner. If it is the head gasket, wouldn't it misfire regardless of unplugging the MAF? My oil doesn't look milky and I'm not losing any coolant from the reservoir.

[Halftim3]

Get a leakdown test. Maybe your head gasket is only blown between cylinder 1 and 2 that's why it isn't misfiring that bad?
Not sure, but yes I believe it would misfire regardless of unplugging the MAF.
I didn't have milky oil or coolant in the cylinders when mine blew and it blew between cylinder 1 and 2, 2 and 3, 4 and 5, and 5 and 6. The gasket is thin in between the cylinders is the reason they blow, but mine only started having the CEL at 209k. It also had the CEL come on after idling a few minutes. I've done some research on it and on another forum someone blew as early as 50-60k miles.

[sapote]

So sounds like the pre-cat O2s need to be replaced then? Or should both pre-cat and post-cat O2 sensors be replaced?.

No, it's too early to think this is due to bad O2 sensor.
I suggest to use a diag tool, i.e. OBD Fusion, which can log all of the sensors data when the issue shows up. With the detail log data we can get to the root cause faster.

[giOsaurus rEx]

So I'm not sure which sensors I should be tracking, but I was messing around with the Schwaben scanner and recorded this.

O2 sensors pre-cat graph during normal idle:


O2 sensors pre-cat graph during misfiring:


Few sensors during normal idle:


Few sensors during misfire:

[CrookedCommie]

Did you ever resolve the issue?

[sapote]

So I'm not sure which sensors I should be tracking, but I was messing around with the Schwaben scanner and recorded this.

O2 sensors pre-cat graph during normal idle:

I didn't followed this thread due to a time gap. But it's pretty useless to show a snap shot of the O2 voltages and the STFT. These data should be logged for at least 30 sec with one sample per second. Also include the LTFT. The MAF unit should be in gram/sec as LBS is too low resolution to tell a difference off bad vs good.