1998 E320 running rough
 

Hi all - I have a 98 E320 with 197k on it. Last week it began to run very rough when in reverse. When I switch to drive or neutral the vibrating stops. Although, this morning with a cold start the reverse was horrible and a slight shake in drive that only lasted a few seconds. In reverse, it getting worse each time. I had a check engine light come on and Check Engine Electronics on the console. Any guesses? Wiring harness? Thanks in advance.