Hello there, I've been looking for solution for few months and finally decided to ask here maybe someone had same problem and can help.
I've got r56 2007 MCS and I've got idle speed fluctuations (it's not as bad as rough idle videos on YT, it doesn't stall, I'd say 50-100), sadly there are no stored faults, here's what I've done so far:
- turbo rebuilt
- new intake pipe (helped a bit)
- new timing chain set
- valves cleaned
- vanos solenoid cleaned
- non return valve cleaned
- TB cleaned
- new plugs, battery, alternator, HPFP and maybe something else I've forgot to mention
When I turn AC on as RPM go a bit higher it makes fluctuations less noticeable.
I've been to few independent shops but with no success.
Any ideas? I'm clueless.

 

I had a similar issue back in the day and it was a fuel injector stuck open.

 

did you get any codes for that?

 

I dont remember i got any codes to be honest which made it frustrating at the time.

I discovered it when I removed my plugs for some reason and noticed gas pooling in one of the cylinders after sitting for a day or so.

 

I found the video i took back then lol

 

mine sounds less rough but i’ll take a look anyway, thanks for ideas

 

Hello,

I'd suggest you check the PCV tube, that runs from rear-passerger side of vavle cover to intake. If this plastice pipe has a crack, there will be a vacuum leak which will cause idle issues.

Good luck

 

small update, today i finally got 2 codes related to superknock (i've got cheap reader but its a clue) so faulty injectors are possibility, i hope it will be fixed finally
i will get back with update later

i've replaced whole valve cover with pcv tube last year so it's not likely the cause but thanks for idea

 

if someone is interested what happened to my car sadly it was cracked piston

 

sorry to hear that bro...is the cylinder wall still in good shape?

 

I've got it fully rebuilt already resleeving included,
i'm during break-in period now, hope i will have some trouble free miles

 

That's awesome bro...how much the sleeving cost you? I was quoted i think 600-800 a cyl!!!

 

Can you please share the details - what was done, how much did it cost, length of time, upgrades or "while-you're in there" stuff?