my 79 450sl developes an engine missfire after getting hot. the misfire feels electrical and will progressively cause the engine to lose power untill you have to pull off the road. if you shut the eng. off and restart, it will run fine for a minute or so, then start missfiring again. when you feel it starting while driving if you quickly turn key off the back on, fast enough that the engine stops then restarts, i guess from the trans. still turning the engine, the miss will be gone for a short period. after a minute or so, the miss returns. the fuel filter, dist. cap , plugs and plug wires have been replaced, as well as the exhaust converter. i need help and would appreciate any ideas. thanks in advance