My 1984 280CE will start after sitting for a while and run for about 1 minute, stall and will not start again. I put a spark tester on the spark plug and found out that it fires but very inconsistantly. If I crank the engine for about 3 seconds it may receive a spark only once on the plug that I am testing. I have replaced the Ignition control module and the Distrubutor cap and rotor along with the ignition wires. Help!