I didn't pick up from your OP that the same mechanic has looked at it multiple times, so it's apparent that he's trying to hold up his end of the deal. A shade tree DIY guy like me would feel mighty uncomfortable making suggestions while looking over the shoulder of a professional mechanic, especially when he's already asked for help from other pros. I believe your current problem is somehow related to the original one or the repair, but that's just speculation on my part. About the only thing I can think of that's fairly obscure, and may be easy to miss is the small MAP sensor connector hose (which was handled during the repair). Others have posted that this hose became brittle, cracked slightly, resulting in hesitation without setting a code. But your problem could of course be 25 or so other things as well. Hope you find the answer soon, and please post back what the problem actually turned out to be.