I had this problem on my 87 300d, and it was worse in cold
weather and when first starting out in the morning.
It WAS the connection to the instrument cluster. Further investigation revealed aftermarket cellular telephone wiring, sourced behind the instrument cluster. The connector wasn't on firmly and just needed to be pushed on more tightly.
Haven't had a problem since.
[This message has been edited by jrd (edited 06-10-2000).]