Ml320 dash lights dim and tach jumps

[Soosoo]

Hi , just had my 2000 Ml in for problems with starting also had a very rough idle, so they replaced the cold crank sensor which seems to have fixed the starting problem, but the dash board lights dim briefly and the tach jumps up after the car has warmed up fully when sitting at a stop sign in idle, it does not die and other than that it run smoothly now, but it is making me think I may have a another expensive repair that I will be dealing with or that it is just going to croak in the middle of the road one day.

Any Idea's ?

Frustrated