2001 windstar hesitates



The engine to my 2001 Windstar seems to hesitate like it is getting too much oxygen or something. Espcially in the winter, I start it up, let it warm up til the RPMs slow down. Drive about 3/4 mile. Stop at a light/stop sign and it almost dies but doesn’t. After it reaches operating temp it’s fine. I have taken it to a trusted mechanic - says it runs lean. Put on the diagnostics machine, says it’s lean. He changed both upper and lower intake manafolds (ouch), fixed hoses that needed to be. Replaced gas caps. I/we are at a loss of what it could be. Suggestions?