Our 1998 E300 had the same problem. The glow plugs were bad. The car would run like crap whenever the car was cold started. It got to the point where it would barely start when cold, and even "warm" starts were effected. I don't know a test, as we had them replaced by the dealer. This seems a common problem with newer MB diesels. No idea why.
1998 C230 "Black Betty"