2002 Ford Windstar intermittent bucking when idling on first start

My Windstar starts bucking and almost stalling when I stop and idle at the first stop light in the morning, about 200 yards from house. Car starts fine, but this happens once I drive and idle at the first stop. This is intermittent and usually doesn’t happen once I drive a few miles. Seems to happen more often during wet or cold weather. Changed plugs, wires, and perform fuel injection service. Problem is getting worse and more frequent. Dealer cannot diagnose problem. Please Help!

Why would you go to a dealer? Unless it is for warranty or recall service they are no better - and are often worse - than a good, local and independent mechanic. They also cost a lot more for not really providing anything better.

Go find a local, non-corporate chain shop. Have them look it over. If they find nothing definitive ask if they can just check and clean the idle air control valve and throttle body.

Is the check engine light on?

No, the check engine light is not on.