im having that same problem with my accord, i have a JDM H22a, the engine had to be incorporated into the stock accord harness, and when i use the stock accord ecu the engine runs like a dream, you know minus the vtec, but when i put in the same ecu, JDM p13, the car idles rough when the engine is cold, and it also backfires, and sputters, i got the ecu from a guy that had it in a modified car, he said it was good but i doubt it, because i can narrow the problem straight to the ecu, i have a cel but thats for the egr valve, and the ecu says that, i just found someone with a chipped p28 with h22 basemap, so maybe by this coming weekend we are going to swap ecus to see if indeed my p13 is bad