I have had the same problem with my 89 190e, lived with it for too long, replaced the OVP relay and it runs like new. Apparently, the faulty relay was the cause of several other problems with my car including the A/C and Cruise Control which now operate perfectly. On my car the relay is behind the panel directly behind the battery. It is the relay with one or more fuses on the top. (old relay had one fuse, the new relay had two fuses) The relay pulls straight up and out of its socket. However, putting the new one required taking out the two relays next to it. Cost of the part was $70 at local MB dealer.