Hey guys, when I start my truck when the engine is cold, it starts and runs fine most of the time. But, when I start it while the engine is warm, it will rev up high, and either nearly stall out, or completely stall out (it has the 5.0 engine). After I put it in gear, the truck runs very rough and shakes the whole thing. At one point, I replaced the idle air control valve with one off of a 4.9 truck to see if it would help, and it did, but it idled a little high. I replaced it with a proper one for the 5.0 and the issue came back.
Could this be the cause of a bad throttle position sensor or vacuum leak? Or am I looking at putting a new ECM in it. Thanks?

 

Does it keep running rough all the time? Or does it smooth out?

 

It smooths out sometimes, but most of the time I have to put it in gear for it to smooth out.

 

Couple of questions as we enter the "throwing part's at the problem"

Have you checked for codes? Has the CEL flashed anytime this problem has presented itself?
You can check for codes with a paperclip.
What PM (Preventive Maintenance) has been performed?

 

No, I have not checked for codes, nor has it thrown a check engine light. The truck has done this since I bought it about three years ago. I do not know of any PM that was done to the truck before I bought it. However, before I bought it, the previous owner had a junkyard ECM put in it because the original one quit working.

 

You are assuming, if you havent checked for codes in 3yrs, does the check engine light, light up, when you turn the key to on but not start it, do you have a Innova 3145 thats the easy button, or you can use a paperclip, and count flashes
Fuel Injection Technical Library » How To Run a Self-Test
(16) How to read a check engine light code on a Ford 1983-1995 EEC 4 system - YouTube