Troubleshooting 325i misfire, rough idle, stumbling on acceleration

[calvarez]

I've done a lot of reading on related topics here for the last couple days, and followed a number of the suggestions, but nothing is quite fitting exactly what I'm running in to. I'd appreciate a little more help.

The car went from running perfectly to doing this in a snap. Literally just driving along and it started running terribly. After some troubleshooting like cleaning the MAF sensor symptoms changed slightly, but not really improved.


Symptoms:

Hunting idle, rough idle.

Seems to be misfiring 1-2 cylinders most of the time then they fire for a split second.

At low RPM (under 3500) during acceleration it has very little power, lots of misfire and surging.

At high RPM (over 3500) acceleration at full throttle is hard and smooth.

At low RPM and no acceleration it runs unevenly all the time, mildly misfiring and surging. Say just cruising along at speed with the CC on, flat road.

Got a DTC code 1222; Oxygen Sensor Lean/Rich Detect (primary): If the signal from the O2 sensor indicates a very lean or very rich mixture for more than 10 seconds, then the computer generates this code. It could mean a faulty O2 sensor, or a problem with another component.

You can smell very rich exhaust at idle (can't sniff it at high speed).

There is NO smoke.

Problem happens from cold start through hot, all speeds.



What I've done:

Removed and cleaned the MAF twice (with CRC MAF cleaner spray). This changed symptoms slightly, but not a fix or major change.

Ran the car at idle with MAF disconnected. The idle was still uneven and going up and down, misfiring.

Ran the car at idle with the VANOS wire disconnected. No change.

Checked and cleaned the crankcase vent line and drain line.

Visual and touch check of the most obvious/reachable vacuum and vent lines.

Check for DTC failure codes, of course.

[Broox]

It sounds like you need a new MAF. But if you dont see any faults for it, that's strange. Try spraying some brake/carb cleaner under the intake at idle. If RPM goes up, replace the crankcase vent valve and hoses. Not a DIY job, by the way.

Also, use a mirror and check the back side of the lower intake boot where it goes into the idle valve for cracks in the rubber.

[calvarez]

Well, I feel kind of silly for not checking this too, but none of the other advice pointed in this direction. Feel free to mete out any noob punishment if it fits.

I decided to pull the plugs to read them, and...

Found one...

WITH NO ELECTRODE!

Sheesh. I'll post a pic tomorrow, now I'm beat and annoyed and need a beer and bed.