You guys are the best, thanks for all the replies! I actually planned on getting myself an OBDII scanner for xmas, so thanks for the recommendation.
The O2 sensor may be it, my mileage is 113,966 (which I meant to put in my initial post.)
I don't know if it was my father or all the auto repair commercials that put the fear of the CEL in my head, but it's good to know I'm not going to explode on the freeway. Traffic would be a mess...
So here's what's what:
Went to aamco this morning and the error code that popped up was P0106: Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance Problem.
He said it could be a hose or sensor, but wanted $100 to scan it with the computer to get a specific diagnosis.
The car still runs fine, no noises, no problems accelerating, so maybe it's just the MAP sensor? I looked online and replacement ones are $35-$50, but I've had this girl long enough to know that labor will do me in regardless.
So that's where I'm at now...
Rule one: stop posting in the general forum.
This is just generic stuff about any and all MB cars. Your car is a W203, so search and post in there.
Rule two: The MB-specific Diagnostic software (SDS) isn't going to do anything more besides extracting $125 plus from your wallet.
The MAP sensor doesn't fail very often, and even when it does it is inexpensive and easy to replace. It's on a little bracket sort of near the idler pulley with a wire and a vacuum line going to it.
Much of the time the vacuum line has degraded and is leaking. So start there, locate the valve and find the vacuum line, then check it for brittleness, cracks, etc. (or just replace the vacuum line). If the vacuum line is good, check the wire connector and make sure it is good. If so, then buy a new MAP sensor and replace it.