2001 mustang gt running rich no check engiine light. backfiring and popping cranks and idles good until engine warms up

hi, i would like to advice you check the electronic idle speed control valve and also check engine coolant temp sensor. The ISC (idle speed control valve) is located somewhere below the throttle valve. the engine coolant temp sensor is located near distributor. it has a two wire connection. the sensor connector is usually green

Could be spark or fuel.
Weak or worn spark plugs, weak coil, dirty injector, and so on.

Check the fuel pressure, and check the fuel pressure regulator while you are doing so. It should be at specification for your car. With engine running, disconnecting the vacuum line from the pressure regulator should make the pressure rise about 5 psi. If any evidence of gas in the vacuum line, the regulator is bad. This is sometimes a cause of running rich. The scanner should be showing fuel trim in negative numbers, as the computer senses too little oxygen in the exhaust, and should be trying to dial the fuel back.
I would go ahead and change the spark plugs now. Make sure that is no problem. And maybe you could spot something from the plug's condition. Of course, if all are black and sooty from running rich, well not much help, but at least you know it's not localized and might help you diagnosing it. Only three things can cause a misfire: either the ignition spark is not good, or the cylinder's compression is significantly lower than other cylinders, or the air/fuel ratio is not correct.

Check vacuum hoses loss or not connected and O2 sensor wires to see if is pinched making a short signal to the CPU.

Make,year,model,engine? don-ohio

Sounds like a coolant sensor problem. It signals the ECU for open loop, cold start rich, high idle, until warm up is reached.

usually when a vehicle backfires, it is caused by the timing or a bad crank sensor. symtoms of a bad coolant sensor are--poor cold idle, stalling, ( rich mixture,retarded timing) slow idle speed, cold hesitation or stumble, and poor fuel milage. check coolant sensor first. good-luck!!

Distributor probably and wiring! Make sure the spark plugs are good and gapped properly!

I would check and make sure your throttle position sensor is working correctly also check your egr valve.

first thing to do is remove spark plugs and if they smell really fuely you will need to change them if that doesnt help you will need to get the microtech tuned for a good coldstart , this depends on if its running stand alone or as a piggy back
cheers.
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