Newbie(I used the search) 420 Stumbles..
 

Hello all,
I am new MB and have a 420 SEL with 190k. All the usuals have been changed. I bought the car with a rough idle. Was initially told it was a bad plug etc. Long story short the mechanic said it was a fuel distributer. Reman unit came in and the idle is perfect. Now it stumbles out the gate(bad). Any ideas??? Thanks!! This was the only part changed.

Because you do not know the history of the car there is not much you can do other than to take it to someone who can do a diagnostics test on it. Who knows who adjusted what while attempting to tune the engine.