97 Altima sputtering issue

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I've had the car in twice to the mechanic, he's scratching his head. It starts sputtering after the engine warms up. It sputters, loses power, kills, then fires right back up. The check engine light does not come on, nothing shows up on the diagnostic computer. He's ruled out the fuel pump and sensor, knows it could possibly be the distributor but I'm not anxious to spend the $300+ without being pretty sure that's the problem. He gave it a major tune up a few months before this problem started. I'm reading a lot on the net from people with very similar problems, but nobody seems to come back and say what they found out.

Ideas?