M135i rough idle

[louder]

Hi guys,

I am in desperate need of help to diagnose my m135i n55 engine rough idle issues. Car has 83k km. Plugs were replaced at 60k km with OEM and the car is completely stock. I can feel the misfires at idle and on light throttle when the car is cold (hesitating) but there are no error codes and I have no idea how to continue.

What I've done until now:
- I've bought an coilpack and moved it over all cylinders, no difference.
- Pumped 2 botttles of European Chevron Techron fuel injector cleaner. Seemed to smooth things a tiny bit but I am not sure if it was placebo or different fuel that caused this
- Tried different fuel stations

I got BMW INSTA and recorded some parameters at idle and at about 2-3k rpm where the imbalance can be felt best. Rough running values seem to be all over the place and I can't pin point what cylinder is faulty. Misfire counters indicate 0 for some reason, although there are misfires almost each second.

Rough running values at idle:
https://www.youtube.com/watch?v=bWiUI0dPozo

Rough running values with throttle input up to 2-3k rpm:
https://www.youtube.com/watch?v=-Mt69SrIPEw

Engine knock sensor values on idle seem off:
https://www.youtube.com/watch?v=4UUDaMn0k8A

Ignition timing is fluctuating 4.5 to 6.75 (is this normal?)

O2 after cat is 0.82V
O2 before cat 1.47V

If any of you have any ideas on how I should proceed I am eager to listen. I've been waiting for this issue to get worse so that it can finally throw an error code but it's already been months and although it seems to be a bit worse, seems it's still not bad enough for BMW technicians.

Thanks

[MarcoZandrini]

The first step in diagnosing a problem is to scan the engine computer (DME in BMWspeak) for codes. You’re getting too deep in the weeds. Scan the DME and post the codes. I bet you have vacuum leaks.

[louder]

I wish it were that easy. I did run a scan but had no engine related codes.

[jclausen]

I'd start looking at injectors, but you may need a more advanced diagnostic reader like the kind shops have auto logic or Ista to run tests

[louder]

- - - Updated - - -

I'd start looking at injectors, but you may need a more advanced diagnostic reader like the kind shops have auto logic or Ista to run tests

I am already using BMW INSTA which I suppose they also use in the dealership. As I said in the original post, the DME misfire counters all indicate 0 and I don't understand why. I am also thinking about the injectors, but they all seem to run in accepted parameters at idle. I am not eager to replace all of them without being sure this is the fault since they are quite expensive. I am not sure what others tests except rough running values and misfire counters I could try.

How could I further diagnose the injectors? I already took 2 plugs out (cylinder 5, 6) and they seemed clean (no fuel/oil smell) and with normal uniform wear (very little because only ~20k km on them). I am thinking about taking rest of plus off and check their state.

Does anyone know why my DME misfire counters seem to not be working? They all indicate 0 and I can't belive that.

[MarcoZandrini]

No codes? That’s odd. I’m wondering if you have vacuum leaks. Can you check on the operation of the pre-catalytic converter oxygen sensors? They trigger lean codes P0171/0174.

[louder]

No codes? That’s odd. I’m wondering if you have vacuum leaks. Can you check on the operation of the pre-catalytic converter oxygen sensors? They trigger lean codes P0171/0174.

1,48V before cat
0.82-0.83 after cat

[Kristopher]

Any update on your progress?

[louder]

Unfortunately I have no progress, so if anyone could share some advices I'd be grateful.

I felt like it's been getting worse, so I plugged in my INSTA again and checked the injector corrections. Seems that all injectors apply a negative correction, values are all over the place but in the accepted interval, so still not triggering a code. I am a bit puzzled. This seems to not be a particular cylinder issue so I was thinking there is an air leak, but in this case shouldn't the corrections be positive? Considering more air si getting in than detected by the MAF?

Oh, the after cat voltage values seem to move a bit more on my last checkup, so again my feelings that it's getting worse are confirmed...