What is the normal idle for 06 mustang 4.0. idles around 600 to 650 in drive.I have noticed that when the AC is on or lights,the idle is a little ruff. And when I'm at a light you can tell when the cooling fan comes on,Idle gets lower and the engine strugles and then it goes back to normal.this mustang has 65,000 miles .

to reset an ECM (CPU) program it will be necessary to use a scanner tool. The idle program is already in the cpu so all it takes is to reset the corrupted cpu program

That is pretty much normal. When the AC engages it's compressor it triggers the idle sensor to increase idle to compensate for the huge load that an AC unit puts on a vehicle. If your AC is producing cold air, approx. 40 degrees on high, then it should be ok. Power loss is all part of the program with AC. It takes much more noticeable power to run an AC unit on a vehicle, and especially a 4 cylinder. Ever see your house lights dim a bit when you turn on the Home AC central air? :.) Every item under your hood connected to your engine steals power from the engine. The AC is the king of all takers of power.

probably cause by the a/c cutting in and out or running at idle . Fit an idle compensator to the system throttle or raise the idle speed 300rpm.

Technically the idle speed is not adjustable. The computer controls idle speed with the idle speed control motor.
Base idle is around 500 RPM with normal idle in park at 800.

Answer - I have a 2012 Toyota Sequoia and the Check Engine light came on and then the Trac Off light came on. The car felt like it was in 4 wheel drive. I read around and found two things that I had to do to get the car fixed.

(1) Clean the gas cap, lubricate the "O" ring around the gas cap, and read the gas cap. It has to click at least once. Make sure there is no gunk around the gas nozzle as well so that the cap and nozzle get a tight seal.

(2) I unscrewed the battery cables positive then negative. I let them be disconnected for 10 minutes. I returned connected the battery and both warning lights were now off and car was back to normal (other than having to reset clocks, radio, etc).

Note: I did notice that the car at first did not idle as it did beforehand. It took a few minutes of me driving around the neighborhood and then the idling returned to normal. Hope this helps.
Daniel

You do not need to reset the computer. The idle speed is low because the computer was reset when the battery was disconnected when the T belt was replaced, the system will slowly adjust the idle back up to the correct speed based on your driving habits, it learns as you drive. It will take about 100 miles.

Gonna give you a list of items that I've come accross with this vehicle same problem.
Hope it helps!
EGR stuck open
battery and cables ( weak and corrosion)
Fuel pressure regulator (stuck open)
PCV valve defective
Fuel pump defective check ball ( little to no residual pressure)

FORD: 1995-96 CONTOUR, CROWN VICTORIA, ESCORT, TAURUS, THUNDERBIRD
1996 MUSTANG LINCOLN-MERCURY: 1995-96 CONTINENTAL, COUGAR, GRAND MARQUIS, MARK VIII, MYSTIQUE, SABLE, TOWN CAR, TRACER LIGHT TRUCK: 1995-96 AEROSTAR, BRONCO, ECONOLINE, F-150-350 SERIES, RANGER, WINDSTAR
1996 EXPLORER This TSB article is being republished in its entirety to include the 1995 4.6L Thunderbird/Cougar. ISSUE: After a 1-4 hour engine soak time, long crank times and/or long crank to start followed by a stall may occur on some vehicles. No further stalling or rough idle will occur after the engine is running. The long crank and/or stall may be due to the Idle Air Control (IAC) Valve sticking.
ACTION: Replace the IAC Valve with a revised IAC Valve if no Diagnostic Trouble Codes (DTCs) are present. Refer to the following Service Procedure for details.
SERVICE PROCEDURE

1. Perform normal diagnostics and correct any DTCs as required by referring to the appropriate year Powertrain Control/Emissions Diagnosis (PC/ED) Service Manual.
2. If no codes are present, replace the IAC Valve by referring to the appropriate model/year Service Manual, Section 03-14. Refer to the following Idle Air Control Valve Application Chart for proper IAC usage.
   
   IDLE AIR CONTROL VALVE APPLICATION CHART Model Year Vehicle Engine Revised Part Number PASSENGER CARS 1995 Escort/Tracer 1.9L F5DZ-9F715-BA 1996 Escort/Tracer 1.9L F6CZ-9F715-BB 1995 Contour/Mystique 2.5L F5RZ-9F715-AB 1996 Contour/Mystique 2.5L F6RZ-9F715-AA 1996 Taurus/Sable 3.0L 4-Valve F5DZ-9F715-DA 1995 Taurus/Sable 3.0L 2-Valve F5DZ-9F715-EA 1996 Taurus/Sable 3.0L 2-Valve F6DZ-9F715-DA 1995 Taurus SHO 3.2L F6DZ-9F715-CA 1996 Taurus SHO 3.4L F6LZ-9F715-AC 1995 Taurus/Sable 3.8L F68Z-9F715-EA 1995 Crown Victoria/Grand Marquis/Town Car 4.6L 2-Valve F5PZ-9F715-AA 1996 Crown Victoria/Grand Marquis/Town Car/Mustang 4.6L 2-Valve F6AZ-9F715-EB 1996 Mustang 4.6L 4-Valve F65Z-9F715-BC 1995-96 Continental 4.6L 4-Valve F5OZ-9F715-AB 1995 Mark VIII 4.6L 4-Valve F3LZ-9F715-AA 1996 Mark VIII 4.6L 4-Valve F6LZ-9F715-AC 1995 Thunderbird/Cougar 4.6L 2-Valve F5PZ-9F715-AA 1996 Thunderbird/Cougar 4.6L 2-Valve F6AZ-9F715-EB LIGHT TRUCKS 1995-96 Ranger 2.3L F5OZ-9F715-AB 1995-96 Ranger 3.0L F67Z-9F715-AA 1995 Aerostar 3.0L F68Z-9F715-DA 1996 Aerostar 3.0L F69Z-9F715-AA 1995-96 Windstar 3.0L F68Z-9F715-DA 1995 Windstar 3.8L F68Z-9F715-EA 1996 Windstar 3.8L F68Z-9F715-CB 1995-96 Econoline/F-150-350 Series/Bronco 4.9L F68Z-9F715-EA 1996 Explorer 5.0L F67Z-9F715-BA

should idle around 700

Your transmission torque converter lock up clutch is not unlocking, that kills the engine and is the cause of the OD light flashing.