2006 R56 Cooper N12 Engine - terrible stuttering

[Krhuangbin]

Wonder if anyone can help....Having serious engine stumbling/juddery acceleration (worse when warm) with the car - it also occasionally stumbles/stalls at idle. When at higher revs and at speed its all OK.

Under load it sometimes will just not accelerate at all, or in very brief spurts, until I change down.

No codes /EML being shown.

I gave it a proper service and changed all the plugs and coils also, to no avail.

The timing chain is OK (I think..!) no rattle and I fitted the longer uprated tensioner recently pre-emptively.

I was thinking MAF sensor but have discovered the Euro cars don't have them....... so would MAP sensor be logical next step?

Any advice/similar experience greatly appreciated

[Sim75]

Turbocharger wastegate vacuum valve?

[Krhuangbin]

Sim75 said:

Turbocharger wastegate vacuum valve?

It's the N12 Standard Cooper engine, so non-turbo. I thought it may be related to the High Pressure Fuel Pump which I read is a common failure, but again, the non-S don't have one.

So not:

-Plugs (new)
-Coils (new)
-Timing Chain (tensioner fine and no rattle...unless previously stretched and timing dodgy? But it's worse when hot....)
-MAF (not present)
-HPFP (not present)
-Also has new rocker cover with PCV value as it was leaking

Can't think what it could be....

[itcaptainslow]

These engines in the DS3 used to be terrible for the inlet valves coking up due to the direct injection. May be worth investigating?

[E-bmw]

These engines are buggers for needing an inlet end de-coke with a walnut blast.

Worth a visit to somewhere that can get an inspection camera down the inlet.

ETA.
That will certainly cause what you are experiencing & (allegedly) needs doing around every 70 - 100K miles.

[Krhuangbin]

Thanks for the above suggestions..... will investigate that!

[itcaptainslow]

As a basic check, a compression test may (only may!) point you in the right direction, too.