A friend of mine has a 99 E430 that runs for apprx 2-6 minutes then shuts down and will crank, but no start. If you wait apprx 10-20 min, it will fire up again. He had it diagnosed as a fuel-pump heat-soak issue, I replaced the pump and filter but the car still shuts off. He purchased the car used in 04 and has done ZERO (literally, zero) maintenance on it. Not even an oil change. The car is in such poor condition I had to vacuum the old airfilter from the filter box When it does run, the engine will rev smoothly from idle to 4K if I apply 25% or less throttle. If I go WOT from idle, it will stumble up to 3K and continue to mis until I release the throttle. I have no code reader, and cannot drive it anywhere to have the codes pulled. My first thought is MAF or cam sensor. Do these symptoms sound familiar to any of you experienced guys? Oh also, there is some nasty sludge/milkshake on the bottom of the oil cap. I remember reading an old post talking about condensation in the M113 and this being normal. Is it?

Most likely a bad crank sensor.

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Are you trying to rev the engine while in park or neutral, or in gear? If it's the former, you may be seeing a feature.

there was a recent post about clogged exhaust precats off the intake at the firewall. sounds similar to his probelm.