1989 300 SEL 207,000 miles, starts and runs for 2-3 secounds and dies, if I manully hold down air sensor plate the engine will run and respond. There is no automatic function of the fuel system.

Sounds like a sensor issue. Replace all the temperature sensors and clean/check the idle control valve. Mine did the exact same thing until I replaced a bunch of that stuff....now it runs fine.

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Thanks, I kind of figure a temp sensor is the problem. If I can keep it running long enough to get to operating temp it will respond to accelerater movements. But there is no power to speak of.