Hello,

My 1993 400sel has begun to idle very strange at times. While I'm at a traffic light, the RPMS will rev up to 1,800 or 2,000 then immediately come back down to 1,200 and the finally back to normal around 800-900. This will repeat itself and the the cycle will go on. This does NOT happen ALL the time. Sometime I will be at a light in "D" and it will just idle normally. Wondering what this could be?

What this is is a sign that you should read your fault codes on the 38 pin diagnostic connector.