[daap1193]

Need some help from the forum members, my M2C with 40,000 kms developed a rough idle some time ago and I'm trying everything to solve it with no luck.
After I stop it takes like 30 seconds to start shaking, it's very slightly to catch on camera but really annoying, I can describe it as a hip cup that feels on the driver seat and repeats every 3-4 sec.

If somebody has experience the same and know what causes will appreciate the help.

What I have tried so far
Check for leaks on the intake system
Clean the maf and tmap
Check all the charge pipes and J pipe for leaks
Replace all the spark plugs and gapped to 0.022

[ASAP]

Coils, injectors and fuel pump / vanos would be my steps...

[doughboy]

Sounds like an occasional idle misfire.

Do you have Ista diagnostics? Misfires can be logged but won't trigger CEL until pretty bad.

There are misfire counters too.

Worth a look.

[F87source]

Originally Posted by daap1193

Need some help from the forum members, my M2C with 40,000 kms developed a rough idle some time ago and I'm trying everything to solve it with no luck.
After I stop it takes like 30 seconds to start shaking, it's very slightly to catch on camera but really annoying, I can describe it as a hip cup that feels on the driver seat and repeats every 3-4 sec.

If somebody has experience the same and know what causes will appreciate the help.

What I have tried so far
Check for leaks on the intake system
Clean the maf and tmap
Check all the charge pipes and J pipe for leaks
Replace all the spark plugs and gapped to 0.022

First do you have any code readings? Next a tune? If so do you have logs?


Could be plug gap, gapping down unnecessarily can cause rough idling and misfires, because of incomplete combustion. Generally you want the largest gap possible while preventing spark blow out, to promote complete combustion.

This is a common issue on bmw's because there is a false assumption going around that the smaller the gap the better, that is not the case. You only run a small gap as a last resort (if unable to upgrade coils/don't want more powerful coils/even the more powerful coils are starting to reach their limits) to combat spark blow out, if possible you want to maximize the gap size.


Depending on your power output you can likely run stock gaps up to around 450whp or more, depending on the state of your coils and your tune. This varies for everyone hence why I recommend starting with a stock gap size and only going down if necessary.

[daap1193]

Originally Posted by doughboy

Sounds like an occasional idle misfire.

Do you have Ista diagnostics? Misfires can be logged but won't trigger CEL until pretty bad.

There are misfire counters too.

Worth a look.

Yes I have ista will look at missfire at idle right now, thanks

[daap1193]

Originally Posted by F87source

First do you have any code readings? Next a tune? If so do you have logs?


Could be plug gap, gapping down unnecessarily can cause rough idling and misfires, because of incomplete combustion. Generally you want the largest gap possible while preventing spark blow out, to promote complete combustion.

This is a common issue on bmw's because there is a false assumption going around that the smaller the gap the better, that is not the case. You only run a small gap as a last resort (if unable to upgrade coils/don't want more powerful coils/even the more powerful coils are starting to reach their limits) to combat spark blow out, if possible you want to maximize the gap size.


Depending on your power output you can likely run stock gaps up to around 450whp or more, depending on the state of your coils and your tune. This varies for everyone hence why I recommend starting with a stock gap size and only going down if necessary.

I'm currently running Bm3 stage 1 multi map, dyno 489 whp. I changed my spark plugs because I had knocking even when on m2 cs map. The rough idle issue persists on any map even when on stock plugs and was there even before I tuned the car. No codes and here is a log on idle.

https://www.bootmod3.net/log?id=619d...729b1a1e2a11cf

That's why I didn't think plugs are the cause but I have an other set that I haven't gap yet will try those out.

I was thinking about cleaning my intake valves (but with just 40k kms don't know if they are that gummed )and also about a pcv/ ccv failure but both jobs are a pain and don't want to spend 600 on a valve cover just to find out it wasn't the problem.

[daap1193]

Originally Posted by doughboy

Sounds like an occasional idle misfire.

Do you have Ista diagnostics? Misfires can be logged but won't trigger CEL until pretty bad.

There are misfire counters too.

Worth a look.

Just check misfires on ista I got multiple counts on cylinder 3. Will be changing my coils tomorrow thanks for the help

[doughboy]

nice bootmod3 log but hard to tell what's what, a lot of yellow lines all the same!

Is the "ignition timing" an advance (pre TDC) figure, just no "-" to clairfy?

[neonbrown]

sorry to revive an old thread daap1193 , your messages are full