I have a 1999 Mustang GT with 86,000 miles on it... I know these sysmtoms are pretty close to "mbhmustang1998" post... The engine runs real bad, choppy only when the engine is cold... Once it is warmed up it runs fine and drives fine. But when I start it up and I don't give the engine time warm up it runs real bad, at about 1500 rpm while driving it, the engine starts tugging. The only way to get it out of the tugging is to let off the gas all together or blip the throttle to go faster. When the engine cold I could some times have the throttle pinned to the ground and there is no response and then all of the sudden it will catch and the rpms finally take and the car moves. I went to a tech guy he plugged in his computer and he told me it was just a bad coil on cylinder 1... Got brand new one from Ford $88.00 and still the same problems. I also put in brand new sparkpugs, same result. Also once the car is warmed up it runs fine but when I shut it off and then go to start it back up while its warm, it shuts right off, then it always starts on the second try. I already replaced the IAC vavle at around 55,000 or 60,000 miles, at that time the car would not start at all, put a new IAC on it started up like a champ. But again even when the engine is cold it always starts right up on the first try every time. Once it warmed up, like I said early, and I go to shut if off and then go to start it up again while its warm it somestimes does not start on the first try, always sarts up on the second. Does it sound like it could be anything else besides a idle air control or dirty MAF?