Cold Start Problem - '91 F150 4.9L

Will crank right up then stall. Have to feather the pedal to keep it going, even then it idles very rough, coughing and sputtering until it warms up. Smokes when first cranking up. When motor is warm will crank right up without trouble.
"Fixes" to date: New fuel filter; new plugs, wires, rotor and cap; new IAC, new cold start sensor, you name it.
No codes. Fuel pressure is fine. Mechanics say it ain't the head gasket either.
After sitting for a few days (4-5) it will crank and jump into high idle and not stall, but will run roughly. If it sits just overnight, will crank and stall.
After it's warm she runs great.

Check the Engine Coolant Temp sensor for accuracy. If it is reading incorrectly, you will get either too much fuel (indicates cold) or too little fuel (indicates warm). Which would account for your symptoms.

Also, be SURE you are getting BATTERY voltage to your coil while cranking.

Already replaced the Coolant Temp Sensor. Is there a way to test it? Concerning the battery voltage - how do you check that, and would it make a difference if the engine was hot or cold?

how many miles are on your oxygen sensors?