I have a 1991 560 sec with 80,000 miles on it. The car is seldom used but is in tip top shape. The other day while driving on the highway, the engine just completly shut off. I tried starting it several times--it would start but die immediatly. After sitting several minutes, it started and drove without a problem. This has happened intermittenly several times now. I had a new distributor cap and rotor on hand so I changed them but the problem continues. I swapped out the OVP relay with aother one to no avail. It starts and will run just fine for long periods then suddenly shuts down. Any suggestions?

J.Chip