Yesterday morning/afternoon I drove my 89 740GL SW 120 miles with no problems. Last night I went out and started it up and found I had a big problem. It idles like it always does at around 800 rpm, but in any gear including park the rpm's drop sharply after it hits 1750-2000 rpm. I can move in reverse and drive slowly, and accelerate smoothly up to that point with no problems, but as soon as it hits that threshold, it dies back, then comes back up, and dies again, over and over. After this, if I release the pedal all the way, it stalls. If i rev it quickly, it'll go above the 2000 rpm mark, but it still dies and tries to come back. My check engine light came on at the point that this happened, and it's still on. I read through the FAQ last night, but didn't see a discussion of this particular problem. The car has 183,000 miles.

Any ideas?