I have a 1990 Bronco with the 5.8 and im at my wits end trying to figure this thing out..Its hard to start when the temp outside is on the cooler side, the fuel pump will sometimes run for awhile then start up ok but after it starts it will run very rough with a little black smoke if i give it gas, if i put it into gear while its running rough it barely goes anywhere so i have to put it in park and wait for it to warm up and then it suddenly clears up and runs like new, but if its warm outside i dont have any of those problems...I have put a new fuel filter on.cap. rotor, plugs, coil, tested fuel pressure and compression and both were fine, i do have a bad TPS sensor but im thinking that with the reaction it has based on how cool or warm it is outside could it be the air charge temp sensor? Please help me!!!!!!!

 

Replace the ECT (Engine Coolant Temperature) sensor. Its mounted above the thermostat in the water neck. You have a "stuck hot" failure I'd be willing to bet my next truck on it. The ACT (Air Charge Temperature) sensor is essentially the same kind of device but less likely to be the culprit as the ECM extrapolates engine temp BEFORE air temp in the processing of the information it is getting. The reason being that if it used air temp as the sole basis for fuel/air mixing, it would always run rich in the cold and always run lean in hot weather.