I have a hesitation problem in my '04 STI. It happens more when cold and at first did not matter when the engine got warm. Now it is getting worse and still hesitates when engine is warm. since the problem started I have changed my plugs(because they needed it anyway). I took the car to subaru and they said it was the rear O2. well i tried to tell them that i dont have a cat conv so what should that matter. to make it worse they did not even check the O2. It was not even hooked up.
I am thinking MAF has maybe gone bad. I cant really find any on the web that arent used and subaru quoted me $200+. I have a perrin C/A intake, and a 3" turboback exhaust. I cleaned O2 but i dont know if it made much of a difference. I did unplug the thing and drove around the block and the problem seemed to do the same thing only worse. I dont know if that was just adding to another problem i have. I have the new software update and do not have any other upgrades. NEBODY have any suggestions?