Here is a shot in the dark, but it happened to mine. I was having a bad idle situation after my (hack) mechanic did some work to my truck. I fought and fought with it, but one day, I got out the brake cleaner and starter spraying around the valve cover to see if there was a vaccuum leak

I would spray at the top of the valve cover, and the engine would rev up. I figured that I had some weird leak on the valve cover. I messed with it and messed with it until I felt the air rushing into the porcupine pipe!!!! The mechanic had apparently stepped on it breaking a 1" hole in the darn thing. I replaced it and the truck has gotten much better about the hesitation, and my check engine light has stopped flashing at me now. I would check for a lean condition from too much air or not enough fuel. I am wanting to say I was getting a code 12 from mine as well.

Just a thought from my experience