Bad MAF? Or something else

[Fabiantir]

Hi all,

Been trying to diagnose some rough idle and performance issues over the last few weeks (posted in here a few weeks back already). Think I may have made some progress in diagnosing and want to sense check my thoughts before dropping £££ on new bits.

Car: 2006 E86, manual, black plastic valve cover N52B30 with 163k miles

Symptoms:

- Slightly rough idle. Rpms fluctuate between about 670 and 730, seems the same whether the car is warm or cold. Seems to be a bit worse on a cold day but I could be imagining that. Tangible shake and an intermittent popping sound a bit like a misfire.

- Exhaust smells rich, especially on startup. Long term fuel trims sit at 6% both banks, short term somewhere between 7% and 10% both banks.

- Engine a bit hesitant at low RPMs, makes changing from 1st to 2nd lumpy.

What I have tried thus far:

- Replaced VVT motor gasket. It was leaking oil and I thought it could be a vacuum leak. Fixed it - no difference.

- Cleaned MAF connectors and MAF, also wrapped a bit of PTFE round the MAF connector to make sure it's snug.

- Unplugged ESS and started engine. Not much difference.

- Checked O2 sensor data at idle. B1S2 swings between 0.8v and 0.1v in the typical way, B2S2 stays quite flat around 0.5v. I unplugged both of them to see if they were messing with the fuelling. No change to idle quality or fuel trims.

- Checked MAF live data. It showed around 4g/s but fluctuated up and down quite a bit. When applying very light throttle, it would dip to around 2.5g/s and then back up as revs increased.

- Reset engine adaptations. Seemed to make a good difference to idle quality and low RPM performance but it was back to normal after a few mins of driving.

- Finally, and what leads me to think it might be the MAF, I unplugged the MAF while the engine was idling and I was monitoring fuel trims. With MAF, short term trims were 7% - 10% as mentioned. Without MAF, both banks instantly swung to about -5%, the idle speed dropped slightly and smoothed out a bit (not entirely though), and the popping sound went away. Plugged MAF back in, trims shot up, popping returned, idle was worse.

Before I hit up autodoc for a new MAF, have I missed anything obvious in diagnosing this? I'm a novice by all accounts, and only had this car for about 7 months. Tried to use lots of info and guidance from various threads on this and other forums, and this is where I've got to. I know there are some wizards on here, so I am willing to listen and try any suggestions to sort this out.

Thanks hugely in advance!

[bigwinn]

Good summary

Did you have an EML or codes at all?

Without sending you down roads that may be spurious I’d check to see if any codes are present then start to look at live reads on things like o2 sensors

[Fabiantir]

Hey, thanks for the reply!

Yes I have had some codes, some consistent and some intermittent.

Had:

- catalyst below efficiency, both banks (this one always comes back)
- MAF signal (only seen once)
- occasional yellow engine light - never affects performance and has always gone away on its own after starting the car a handful of times
- knock sensor code (only seen once)
- big DISA self diagnosis (only seen once)
- VVT adjustment (was because I didn't quite line it up, refitted carefully and code hasn't come back yet)

+ a few other unrelated ones like parking sensor, window anti trap, seat heating undervoltage

In my previous post I thought I could have some battery issues considering the non-engine related codes. Admittedly I still haven't changed it, but my latest round of diagnosis (i.e. poking stuff and seeing what happens) seemed to point me towards the MAF rather than battery hence the new post

[bigwinn]

Hm

You run the risk of buying a load of different parts and chucking money at it: and genuine MAFs aren’t cheap

Anyone near you to swap one over to see if that helps?

[Fabiantir]

This is what I want to avoid especially with MAFs being fairly ruinous. I'm based in Essex, just outside London. I've seen a handful of Z4s around but not sure if they're local or just passing through. Is there an owner map or something on here?

[bigwinn]

I can’t immediately think of anyone in Essex with an n52 3.0

May be worth popping a post up

[Fabiantir]

Yes looks like it. Perhaps a silly question, but would the MAF in an E86 be the same as any other N52 engined BMW?

[bigwinn]

Check realoem

I was just thinking if you can fit an n52 2.5 maf you’ll widen your opportunity

[bigwinn]

https://www.realoem.com/bmw/enUS/partgr ... MW-Z4_30si

[Fabiantir]

Alrighty, will post on here soon and maybe on FB as well to see if someone is willing to do a brief MAF swap

Any other easy/free steps I can try to narrow it down while I look for someone?

[TrackMyZ]

I thought I would share the diagnostic hell that I went through. I had wicked idle problems but had a mass air sensor only a couple of months old. Then I get a Vanos error so I replaced the solenoids. Seem to be running well for a day and then all the sudden it started idling like crap but running well when speed is up. But Idling problem continued and performance started tanking. So then I went through the long list…. Replaced six month old plugs, then tested coil packs and 2 six month old ones looked flaky, replaced those. Still rough idle. Checked solenoids again and put the bmw one back in. Checked vanos sensor (major pain) , Replaced mass air sensor anyway. I was getting an engine light but no errors because after solenoids I reset ecu and it took awhile. Then I found it because the leak finally got bad enough. I read that any form of gasket leak can cause all kinds of different things to stop working. Mess up solenoid, and plugs. What a pain in the ass. To make matters worse the last time I had the oil changed they spilled some so when I cleaned everything off after pulling the plugs, I didn’t realize it was a combination of oil spilt from the top, but also oil was coming out of the valvetronic motor seal. At this point, the leak had gotten so bad that when I went to check the plugs again, it had filled up the crevices around it. Easy fix and now she’s happy. When I think about how many times I checked and pulled those solenoids.

[Fabiantir]

I saw a video of someone having this same exact issue with the VVT motor gasket too so I've tried replacing that to no avail. Tried pulling and cleaning the solenoids recently and that seemed to improve it a tiny bit (could be a placebo). Thinking next will be pull the vanos filters and have a look, and after that I think I will need to smoke test it. I've been putting that off out of sheer laziness to get the bits needed to get it done