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I'm at a loss. My car is throwing a code indicating it's running rich in bank 1. It stutters or hesitates at idle sometimes and can't hold ~1500 rpm if I just give a little of throttle with the clutch in while stopped, but stutters or hesitates slightly around that RPM.
2012 N18 MCS with 230,000 km, mostly stock.
This is similar to how it would run when the turbo inlet hose slipped off, but I've fixed that issue and am pretty certain there are no vacuum leaks along the intake hose to the turbo.
Could this be a cracked valve cover or gasket? How can I check that?
Is there any way to tell if I have a faulty MAF? I've tried cleaning it with MAF cleaner to no effect.
If my intake valves are all caked up would this cause the problem I'm seeing? (I haven't walnut blasted them and don't know what shape they're in).
Is it possible a bad downstream o2 sensor could cause this? It was replaced not too long ago so unless it's gotten fouled up due to other problems, I don't think it's that.
I do have a leak in my exhaust at the flex tube, but I'm waiting on a new down pipe and exhaust to arrive so I can't fix that until those parts arrive.
I just installed a cheap amazon boost gauge, and it's reading almost no vacuum and up to 22 psi boost on a stock tune. I have the NM power module installed, but even with that I think I would only get up to 17 PSI boost. Is this amazon gauge just reading wrong, or is it possible that it's showing I have a vacuum leak. Why would it show up to 22 psi though... that doesn't seem like it should be possible.
I welcome any suggestions. I'm at a loss at this point!
What codes are you getting? When you scan the car; scan it in OBDII and post the OBD codes.
You have nearly 143,000 miles on the car and you've never had the intake valves cleaned? Get that done ASAP! Yes, coking on the intake valves will cause poor engine performance at all power settings.
Yes, you can connect a lab scope to the signal wire on the MAF sensor and measure the frequency. You should see 1.9Khz at idle, and about 5.1Khz at WOT.
You can test the downstream O2 sensor to see if it's functioning, but remember the upstream is a wide-band sensor, and the downstream sensor is narrow band. So, you'll be looking for current switching on the upstream and a steady 725mv singnal on the downstream. A fixed lean upstream O2 sensor will cause a rich command from the DME, and the car will run rich.
Valvetronic engines don't product much vacuum at idle because the intake valve lift is so little at idle; for example a standard engine without variable valve timing or variable valve lift will run 18-20 in of vacuum. BMW/MINI valvetronic engines run at less than 1" of vacuum. That's why you don't see any vacuum.
I don't have a scope but my OBDII reader interprets the airflow rates from the MAF as 3-5 g/s at idle (more like 3 right now if I recall) and 130-140 g/s under full load. I will see if I can get the raw data somehow.
*sigh* When I looked at walnut blasting in the past it was either expensive to get done, or fairly challenging to DIY. I will have to see what I can do. Especially considering I'm trying to get the car ready for a turbo upgrade.
About the vacuum -- that's really helpful information! IIRC my '97 A4 was showing about 5 psi of vacuum, but I suppose that's a different story.
Ok. So does your OBDII reader allow you to see fuel trims? If so, check your fuel trims (Short term & long term STFT<FT) at idle. Write the numbers down. Then raise the engine RPM to 2500; record the STFT/LTFT numbers again; post them here
The -24 LTFT number means the DME is pulling fuel away from the engine (Rich condition/lean command from DME) Now if you add the STFT and LTFT you get total fuel trim of -23.5 at idle. Notice at 2000 RPM your total fuel trim is -21.8, at 2500 your total is -14. In ideal conditions (brand new engine) your STFT and LTFT numbers would be close to zero at all RMP ranges. Your engine is starving for air.
1. Check your air filter and make sure it's clean.
2. Check MAF Frequency against the numbers I posted earlier. Sorry, the manual doesn't give a g/sec specification; it only gives frequency at idle.
3. Pull the intake and inspect the intake valves; if there is a lot of carbon build up, that will restrict air flow; less air flow means less fuel to maintain a Lamda of 1 (14.7-1 air/fuel ratio).
Remember, if the intake valves have a lot of carbon build up; it will restrict the airflow into the combustion chamber, and that will show up on the MAF sensor reading. Meaning, you might have a perfectly functioning MAF sensor, but it will give false readings if the intake valves are restricting airflow.
Well, my air filter was extremely dirty and I couldn't find the k&n cleaner products at my local store so I put on a new cone filter. Slightly larger/longer, so presumably if the dirty filter was causing my issue this should have resolved it.
With new filter my LTFT went to -30 at idle but comes up to -11 while driving.
One thing I forgot is that NM power module might be adjusting my MAF readings. I don't know if it just reads them or reads and changes it like it does for the boost.
Likely going to try get replacing the MAF even though my readings are consistent with yours
Disconnect the MAF and see what happens to your fuel trims and how the car runs. Some cars have a default strategy for a MAF sensor failure; some don't. Before you throw money at the MAF; pull the intake and look at the valves.
Well I replaced the MAF and it didn't immediately solve my issue, fuel trim was still -30% at idle but I took it for a drive anyway and after that, the fuel trim was at -10%. I also noticed the MAF was reading more like 1.7-2 g/s
I read that LTFT responds to readings from the down stream o2 sensor, so I took it out (while still warm mind you) and sprayed the crap out of it with MAF cleaner.
After you changed the MAF you have to compare the LTFT and the STFT. For example: If you have -30 LFTF and 30 STFT, that means you fixed the problem. -30 + 30 = zero ... perfect fuel trim. Over time, you'll see a negative LFTT come back to zero with a positive STFT.
When you went for your drive, the engine computer was correcting; that's why your number went from -30 to -10. It looks like the MAF was your problem.
You read that LTFT responds to the downstream O2 sensor; I would love to read the BMW/MINI technical manual that says that. Not saying it's not possible .... only that I'd like to read it. The downstream O2 is typically used to determine catalyst efficiency.
It was -30% combined, initially after changing the MAF. I didn't how long it would take for the long term fuel trim to adjust, but it did seem like it required driving it in order for it to adjust to the new MAF. Initially, I had let it idle for 10 minutes thinking it might just need more time but it wasn't changing, until after I drove it. Even then, it had only settled to -10% (combined) after a short drive. I do suspect cleaning the o2 sensor also helped, but who knows, maybe I just didn't give it enough time.
And yeah, I fibbed a bit when I said I read that the downstream o2 sensor was used to adjust LTFT. I had asked my google home about my issue and that was the response -- no idea what website or for what car the information was.
It doesn't quite say that the downstream o2 sensor is responsible for adjusting LTFT, but it may end up having that effect due to the "smoothing" or "averaging" effect of the catalytic converter? I'm not quite sure-- I'll have to re-read that pdf again at some point. Lots of interesting/useful information in there, I think.
