Our early Gen 2 R56 Cooper has been misfiring/hesitating at 2350 - 2400rpm for a few months. Once clear of the misfire/hesitation above 3000rpm it runs smoothly but is down on power. There is a change in engine note at 2400rpm as if an engine management setting changes at this engine speed. Various investigations have been undertaken but no solution as yet.

The car starts fine and idles smoothly. It has covered 63k miles and doesn’t burn much oil. Between idle and 2300rpm the engine feels normal. As an early R56 Cooper (non-S), there is no Mass Airflow Sensor fitted before the throttle body.

No diagnostic fault codes are present on Autel MaxiDiag Elite reader but its Load graph shows a clear dip when driving through 2350 -2400 rpm with Wide Open Throttle.

New plugs fitted. New coils fitted. New MAP sensor. Running without the air-filter makes no difference. A VANOS actuator was also recently replaced. Throttle body operates smoothly from closed to wide open. No vac leaks identified.

PCV Valve in valve cover does not appear to present any resistance in either direction, i.e. air can flow freely in and out – is this normal? However, it makes no difference to the hesitation if the PCV line is temporarily blocked.

Has anyone come across this before? I’m running out of ideas. Any suggestions much appreciated!

Thanks, Dave

 

did you replace spark plugs?

 

Yes - spark plugs changed before other components. Improved starting but hestitation remained. Not sorted yet.

 

I know you said you changed the vanos actuator, but did you check the vanos solenoids. There are two pieces back and front of cylinder head passenger side.

 

Start with finding a quality scan tool or a shop that has one. You need to read the stored fault codes before you begin to throw money at the car.

VANOS solenoids can cause weird lumpy idles as well as low power, but so can multiple other problems.