New at this so here goes, have 1992 f150,4.9 manual trans. slowly over the last couple of months i have been having trouble while driving, the motor revs and misfires and when you step on gas pedal it gets worse. Cleaned IAC and disconnected battery to clear ECM. Started truck and let run for about 20 min. Truck ran fine but when i pushed on the pedal to rev the engine the motor reved and wouldn't return to normal idle, misfireing all the way. Don't want to buy a bunch of new parts just to fix one. Have multitester but limited to just test probes.

 

Check for vacuum leaks. Check the codes. EGR might be an issue.

 

ok, 1992 f150 4.9 2wd: Well lets see now, was doing an koeo test when IAC started to chatter, ok, maybe that's the problem so decided to check harness voltage, next the plug removed and turned on key, next thing that happened was a clicking noise near the coil and Dist., fuel pump kicks in and runs and runs and i turn key back off. hello, sound familiar? let me know. Had 12 volts at plug so is getting power. But hadn't noticed other problems until IAC was unplugged.

Update, truck runs fine when cold, drove it the morning and ran fine but then it seems when the truck warmed up i started to have the same problem, checked water temp module and it has the correct voltage and ohms in range.

 

Well after testing ref voltage on multiple harness plugs, getting vauge or useless advice on what the problem could be, since computer was not throwing codes pulled pcm and found multiple fried resistors, capacitors and have concluded that my truck needs a new pcm.

 

I would also check the alternator before putting a new PCM in.