I hope you can help me. I have a 2002 Buick Lesabre with less than 100,000 miles on it. When I start it up in the engine will run will ruff and the check engine light will flash on and off. I put the car in gear and start to move the car about a minute latter or so the car smooths out and the check engine light goes off.  When I start the car the rest of the day it starts up and runs perfectly.  My mechanic replaced the purge valve and it solved the problem for a little bit and started back again. I took it to him he put another one in and the same thing. It than started acting up again and I took it to him and he checked the purge valve and it was closed. He said most of the time the car doesn't act up enough to kick out a code. I took the car to him today and told him I didn't want it back until it was fixed.  The Buick lesabre group thought it might be a MAP sensor but he didn't think so. I really love the car and don't want to get rid of it but this problem is making me crazy.  
Any help you can give me would certainly be helpful.

Thank You

Steven Allen