Joe, On my 1985 2.3 190e the OVP is located directly behind the battery near the firewall. It is silver in color with a red top that houses a fuse. It's about 2 inches tall and simply plugs into a socket. Beside it is a small black box which is the fuel pump relay (it should have "kickdown" written on the top of it). When you locate the OVP be sure to remove the fuse and check it before replacing the OVP.
A bad OVP in my car caused symptoms similar to what you described. Very easy to replace and can be bought at Fastlane for around $60.00.