I have a 2000 mustang GT.... just bought the car and rebuilt the motor. The motor is all stock except for the Cold Air Intake (K&N air filter) The idle problem was there before the rebuild. I have checked the following, all vacum hoses, sprayed carb cleaner all around did not find any leaks, the car has no check engine light or codes.I have checked the tbs and ohemd it out (fine), checked the idle control valve, ohmed it out& cleaned it and it seems to be working fine. I can hear it clicking when i turn the key on. The mass air flow sensor I thought could be bad so I had one from a 2001 mustang and it ran worse so, put the other back on.But if you unplug it (mass air flow sensor) it idles fine.I could use any help, I have a lot of time and money in this car