[danwiththebmwproblem]

Edit for anyone coming across this post later on, wondering if/how I fixed this:

The technician found lots of broken bits of plastic from the timing chain guides in the sump so we went ahead with replacing the timing chain, guides, oil pressure control valve, oil pressure sensor, sump gasket, valve cover gasket, and front crank seal. Also new oil and filter

I'm not sure if this was related, but I also got all new injectors because I'd had issues in the past with them anyway and labor was free.

Car now runs decently, I've driven about 60 miles and no issues yet. Will update if things go south..

Original post:

Car: 2009 BMW 320i, E92 (170BHP / N43), 160,000 miles

Symptoms:
Rough idle that doesn't trigger an EML or error code. Doesn't go away when car is warm. When car starts cold RPMs go up to 1000 for about 20 seconds (not rough idle), then drop to 700 (rough starts). The RPMs then seem to lag down to 600, jump back up, lag down to 600, jump back up, etc. Car also has a long crank time, but this has been present before the rough idle.
Probably unrelated error code - 30C1 oil pressure control, static

Car history:
Had a cylinder 1 misfire that went away when the car was warm that I didn't bother to fix for 2 years. Got it fixed in January. It was fixed by replacing the injector and coil in cylinder 1, along with all spark plugs.
This issue seemed to appear around that time period, but it might've happened in the month before, not immediately after the repair (I remember noticing a rough idle when the car was warm but not sure if it was before or after...)

Garage diagnostics:
Check fault code history - nothing
Run fuel injector diagnosis scan - results:

Operational smoothness value, cylinder 1 (setpoint value -200 to 200):
105.10

Operational smoothness value, cylinder 2 (setpoint value -200 to 200):
-103.00

Operational smoothness value, cylinder 3 (setpoint value -200 to 200):
23.10

Operational smoothness value, cylinder 4 (setpoint value -200 to 200):
-25.30

Run oil pressure control system test 4 times, pass

Garage recommendation:
For rough idle - Replace other 3 fuel injectors (not spark plugs and coils)
For 30C1 - replace oil pressure control valve, clean valves and solenoids (or maybe replace, still waiting on them sending over an email with specifics). Since this is a lot of labour to take parts off to get to, may as well replace the timing chain at the same time

Questions:

Garage seem very confident the injectors will fix the issue. I feel like it's an expensive route to take before checking coils or some other cheaper option. It's their level of confidence that makes me skeptical -- they don't seem to think it could be anything else. Of course, they might be right, I don't know much about cars, just it's a new garage and didn't want to accept a costly repair blindly. Does it sound like injectors are the right thing to replace here?

The 30C1 diagnostic result seems appropriate. But just want to check that there isn't something else you'd recommend doing? All I've done in an attempt to fix is get the oil changed. My concern is that I'll pay this repair bill and then find out it's something else that'll be worth more than the car.

Also, I'm treating the rough idle and oil like two different issues that aren't linked. Does that seem sensible? Initially I thought they were related but the garage thinks they aren't.

[MadJoe]

Have your flywheel checked. When mine went bad it didn't throw any codes and it caused a weird rough idle I wasn't able to track down until I found the tell-tale grease the flywheel crapped out. But it didn't crap that out for a few weeks after the symptoms started, so there may not be any and it could still be bad.

[danwiththebmwproblem]

Originally Posted by MadJoe

Have your flywheel checked. When mine went bad it didn't throw any codes and it caused a weird rough idle I wasn't able to track down until I found the tell-tale grease the flywheel crapped out. But it didn't crap that out for a few weeks after the symptoms started, so there may not be any and it could still be bad.

Thanks for the response! Are there high labor costs on checking the flywheel?

[MadJoe]

I would expect it to cost ~1hr of labor, whatever their hourly charge is. It shouldn't be too much, but you can always ask before agreeing to the service.

Just be aware that if it is the flywheel the part costs ~$700 before markup and labor. If you do it yourself, which isn't too tough assuming you have the tools and space to do it, you can avoid the markup and labor obviously.

There are kits to switch it over to a regular (non-dual mass) flywheel that cost about $500-$600 and then you should never have a problem with it again. The trade off for that is that your city mileage and low-end performance may take a small hit due to the flywheel feeling "heavier" to the engine at lower RPMs.