I have the same car, did the same thing you describe. Idle speed control switch fixed mine. It has a little rotating "door" per say and mine would stick occasionally resulting in the engine dying. At the end of the switch is an exposed shaft about 3/16 in diameter. Mine had rust on it, clean off the rust, lubricated it with some spray lubricant and then took the leads to battery to make the switch open and close several times. Has been working fine ever since (it's been over two years). Good luck!

Eric.

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90 300TE
00 ML320