When my 99 ML320 is cold it starts and runs perfectly. When it has run a few minutes it will suddenly shut down and I have to let it cool down for ten minutes or so until it starts again. It turns over fine but will not fire. It will sometimes drive fine for a few miles but when I stop and turn off the engine it will not start. After it cools down it starts ok. The "check engine" light does not come on. I took it to a local mechanic but he can't get it to repeat the behaviour. Any ideas as to what is going on would be very appreciated. Terry