Misfire on start hot and cold

[dayvision]

My 128i was in the parked garage for ~18months. Finally got it all back together but I had a misfire issue I managed to fix, before finding a new one. The old issue was a bad o2 sensor, post cat on the second bank, I was getting error codes for cylinder 4, 5, and 6. When I pulled the sensor it started up just fine, beautifully even.

A week later I install the new sensor and now when it starts up it misfires and wont idle. if I give it some throttle to keep it alive it will, after 1-2 minutes, stop misfiring and idle normally at around 600-650 rpm. At this point it drives fine, all smooth no loss in power or anything. If I shut it off and immediately start it up it misfires again for 1-2 minutes.

Codes (some may be old but they won't clear):
P00bc - MAF error
P0301 - cylinder 1 misfire
P0306 - Cylinder 6 misfire
P0300 - multiple or random system misfire
P0056 - bank 2 sensor 2 o2 sensor not heating up properly
P0172 - rich fuel

New spark plugs
new bank 2 post cat o2 sensor
Even tried swapping this out again but no luck
new battery
new gas with fuel injector cleaner
Cleaned MAF

I swapped out the ignition coils, full set, a few years ago so they have maybe 30k miles on them.

I'm really at a loss here now. It should be something with the fuel, air, ignition or exhaust and the fact that it fixes itself suggests to me its something downstream but nothing changes if I disconnect or swap out the o2 sensor. Maybe a bad connection to the sensor? but then I'd expect the whole bank to have issues.

Any ideas?

[///Makis]

Originally Posted by dayvision

My 128i was in the parked garage for ~18months. Finally got it all back together but I had a misfire issue I managed to fix, before finding a new one. The old issue was a bad o2 sensor, post cat on the second bank, I was getting error codes for cylinder 4, 5, and 6. When I pulled the sensor it started up just fine, beautifully even.

A week later I install the new sensor and now when it starts up it misfires and wont idle. if I give it some throttle to keep it alive it will, after 1-2 minutes, stop misfiring and idle normally at around 600-650 rpm. At this point it drives fine, all smooth no loss in power or anything. If I shut it off and immediately start it up it misfires again for 1-2 minutes.

Codes (some may be old but they won't clear):
P00bc - MAF error
P0301 - cylinder 1 misfire
P0306 - Cylinder 6 misfire
P0300 - multiple or random system misfire
P0056 - bank 2 sensor 2 o2 sensor not heating up properly
P0172 - rich fuel

New spark plugs
new bank 2 post cat o2 sensor
Even tried swapping this out again but no luck
new battery
new gas with fuel injector cleaner
Cleaned MAF

I swapped out the ignition coils, full set, a few years ago so they have maybe 30k miles on them.

I'm really at a loss here now. It should be something with the fuel, air, ignition or exhaust and the fact that it fixes itself suggests to me its something downstream but nothing changes if I disconnect or swap out the o2 sensor. Maybe a bad connection to the sensor? but then I'd expect the whole bank to have issues.

Any ideas?

Try unplugging the maf and starting the car.

I think it runs on closed loop when the maf is unplugged.

If it idles and runs fine then the issue may be related to o2 sensors or serious vacuum leak, or a/f In general.

If it still idles like shit and doesn't run at all, then I'd say check the plugs and coils and any electric connections.

You say finally got it all back together, what did you take apart?

I did the 3 stage intake swap and forgot to plug in a vacuum line under the manifold. The car ran fine when I started it because I did not plug in the maf sensor, when I realized I didn't and plugged it back in, the idle was horrendous and the car stalled and would not run. I ended up taking the whole thing off again before I realized what it was.

So try unplugging the maf and see what happens

[lvfb]

before doing all that. check if you have the N51 engine as that is a SULEV engine and most of the stuff you just typed is covered under warranty for 15 years or 150k miles