2000 windstar lx

I have a 2000 windstar lx with 80,000 miles. For some reason the van occasionally stalls out and when I try and start it it sounds flooded or choking. I have had it in shop twice and they cant find anything wrong. Because by the time it gets towed in it will start like nothing is wrong at all. This has happened on 6 occasions over last year and does not set any fault codes in computer. Does anyone have any suggestions on what this might be?