I just recently got another 1990 bronco with a 351, and it started when i bought it then drove it 30 miles, parked it overnight and then tried to start it, it cranks revs up and them back down then continues to crank. It has a new distributor, plugs, wires, ignition switch, coil, fuel pump and relay. The guy bypassed the inertia switch i saw and cant find the wires for it to check. I couldn't figure it out so i gave it to the mechanic and he checked spark, fuel pressure and connections then it started right up then i drove it home and tried to start it the next morning and still nothing. I was thinking of buying a new IAC just incase its stuck in open or close, and i have tried to start while pumping the gas pedal and putters then continues to crank. The mechanic said it sounds like a misfire when it starts as well. Any help would be greatly appreciated.