I recall a '96 SL500 that wouldn't set the EGR portion of the three [Catalyst, EGR System, and Secondary Air System ] monitors, if I remember correctly. Try as they might, it wouldn't come "ready". This went on for weeks.
Finally had to remove one head (left side I think?) b/c of just enough carbon build-up in the small passages to cause this puppy to never come "ready". There were no codes!
Remind me to NEVER buy a '96 - '99 MB . .
