1995 Ford Mustang • 128,000 miles

At normal cruising speed, take your foot off gas, you expect car to slow down but it doesnt. It takes a good 10 15 seconds for the car to get off the gas and slow down. Also rpms stay up in between gears. 5 speed. Replaced idle air control valve. No change. If I just unplug idle air valve, it runs a little rich but it doesnt drive me crazy. Any ideas on where to go from here, its time for a smog check, so im in a little bit of a pickle.
October 25, 2012.

When did this start to be a problem?

Dr. Hagerty
Oct 25, 2012.
I just got the car couple of weeks ago. When I got it, it needed a fuel pump. I replaced it, and noticed the problem. The owner before me, unfortunatly, didnt know a whole lot about cars but had himself convinced that he was a mechanic. Thus im sure everything is out of adjustment. I simply unplug the idle air valve for fair driving. But plug it in its like a giant vacuum leak. Ive checked everywhere. Ive replaced the following.
Idle air control valve
intake air temp
coolant temp
throttle position
mass airflow
cap, rotor, coil
im begining to blame the computer, but which one. This is my frustration
thank you for your help and knowledge, its appreciated.

Oct 27, 2012.
I would start with looking at the operating parameters, all the inputs to the PCM and compare what is found to a normal reading.

Dr. Hagerty
Oct 31, 2012.