91 f150 4x4 5.8 motor. It was running fine then it started sputtering on the road. I thought it initially jumped time, however it will idle correctly. I also replaced the transmission, AIC and rotor cap and such. It will almost immediately die with it is put in gear....

 

Change the fuel filter, check the fuel pressure. Check the exhaust and cats for blockage.

Does "and such" include plugs and wires?

 

Your 91 5.8L was the first year for the IAB (Idle Air Bypass) which you've identified as the IAC. During the first half of production for the model year, there was no spacer plate between the throttle body and the IAB. If you don't have one, get one. This little device than looks like it's a nothing is very important to the idling and prevents the deposits buildup at the IAB. You should have a minimum of 10.8 volts at the IAB. If not, you probably have a bad EECM. The EECM is what provides voltage to the IAB. The IAB is not a sensor but a servo motor that allows air past the throttle body to maintain idle while under load or not. Apparently yours is not working right.

As a test, if want to try it, look under the plastic shroud of the throttle body. You'll find an idle screw. You can mark and remember the exact setting before adjusting it. Then turn it up to idle the engine up to about 1000 rpm. Start the engine, stand on the brakes and drop in gear. It will probably continue to run. If so, the IAB and EECM are not talking to each other. It can be a bad IAB even though it's a new part or it can be a bad EECM. You can get a replacement EECM at NAPA for a little over 200 bucks already to go for your engine but you'll need the VIN for the parts guy to get the right one.

FWIW, if you didn't or haven't cleaned the throttle body, this can also be an issue. Replacing the IAB and not cleaning the throttle body buys you the same problem. The throttle body MUST be removed to clean. DO NOT spray any cleaner in the throttle body while on the engine. If you do, expect to have to replace all of the intake manifold gaskets as you will have an uncontrollable high idle. The cleaner will destroy the gaskets. The throttle bodys on these engines must be cleaned every few years as deposits that are blown back via the cam overlap will render the IAB useless and stalling will happen. You'll need a throttle body gasket if cleaning it.

 

I also forgot to mention that the OD light also flashes.....I rebuilt the transmission and it only has about 2 miles on it......the IAB that I replaced seems to be working correctly because you can now hear the "sucking" noise from the air intake...so I did not think that it could be the EECM. I will try cleaning the throttle body and see if that will help any....this thing has be stumped!

 

If the OD light flashes, you need to read out the codes.