It looks like I need some unscheduled maintenance.

I had my check engine light pop on on Tuesday, and the car was difficult to start the following morning. I contacted my SA, and he suggested that I see if it clears itself prior to bringing the car in. Sure enough, the light cleared itself in about a day. However, it popped back on about 24 hours later.

I realize that the CEL is pretty much an emissions related warning, and the car appears to run fine on the surface. However, I seem to notice that the throttle response is a bit off, alternating between sluggish and overreacting to my foot on the pedal. The effect is subtle, almost subtle enough to cause me to think it is psychological.

I'm guessing that a sensor is going bad, and causing the idle issues.

Unrelated to this, I also hear a groaning noise from the engine at low RPM, particularly when it is cold. I think it might be the power steering pump, as it is more pronounced in corners where both the power steering and the ARS is placing demands upon on the pump. Since I'm going to be taking the car in for the prior issue, I might as well enquire about this as well.

Has anyone heard of or had any similar problems? Any information would be appreciated so I can get the most out of my service visit.

On my E90 I had an intermittant CEL and it turned out to be a bad camshaft sensor. Car seemed to run OK when the light was on. The dealer diagnosed the problem quickly as the fault codes are saved.

Thanks. I'm guessing it's something similar.

Congrats! You win the prize!

On of the four camshaft position sensors died. They're replacing all four, and I'll get my car back tomorrow.