If I have the engine running with my car stationary in "park" position, I step lightly on the accelerator pedal and hold at anywhere above smooth idling and below about 2000rpm, the engine kinda "flutters" (don't know the exact word to describe it). It's like you can feel very minute misfirings, or as if there is this "bubbling" feel like in the old engines running with the choke lever on. When I step on it more and bring the rpm up past 2000, it runs normal.
Same thing when the car is running in gear and moving from stationary or cruising slow below 2000rpm, except that I don't feel it that much unless I pay close attention to it.
Has anybody experienced this before? Is this normal, I don't think it is.
It might have something to do with the "Service Engine Soon" light that is on now and that I'm trying to figure out what the fault is. DIS showed a vague "fuel mixture too lean or rich" problem. I had just replaced a faulty oil separator and thought that was it, but the light came back on.
By the way, it's a 2000 540iA