Okay, I have been a chevy guy forever, and respectfully a dodge enthusiast..
I have decided to give ole Ford a try.. so far not so good, However I have not lost faith yet. so heres my problem..
My 1993 F150 XLT 4x4 with the 5.0 is having issues..
truck has 89K with 18K on tranny.. now 89K could be 189 or 89 but no oil leaks ect an it sounds great...
main issue engine light, start the truck in the morning while cold, voltage level jumps up and down and RPM's drop its ruff, alt was tested an is fine, so after about 3 to 5 seconds engine light comes on, truck warms a bit or you drive a bit an its fine, shut off good to go start up 3 to 5 seconds engine light comes on, ok, now you go down the road get into third gear at a low RPM any gear for that matter, use the throttle over RPMs to speed back up so don't down shift, engine light goes off truck loses power bucks jumps an revs funny, then just loses speed till you let off gas engine light comes back on you down shift an get the RPM's up an be sure not to over throttle an it goes along just fine.. any ideas? I don't want to put to much money in this truck yet.. because I can't get it inspected without body work being done... I don't want to do body work unless engine light issue is fixed.. sorry about the letter, but it has me stumped idles ok most of the time, runs fine except for this, and I have driven about 500+ miles like this... now it was sitting for a few months prior to sitting no engine light on.. no issue.. Thanks!!

 

I'm no mechanic but I would try cleaning the EFI system... throttle body, fuel filter, air filter, mass airflow sensor. Run some good gas with some fuel injector cleaner in it. Might even do the whole sea foam operation as well. I don't know much about that engine but that is where I would start.

 

I think , from the sounds of it anyway, I'd check for vacuum leaks.
clean or replace the IAC (Idle Air Control).

If the CEL (Check Engine Light) is coming on, even intermittently, I also have the codes scanned....usually can get this done down at your local parts store. Then post what they are so the good folks can help direct you towards a solution and not just throw parts at it.

I'd also have the alternator checked for proper function and output...not sure if the erratic idle is fluctuating the voltage output or weather the alternator output is affecting the erratic idle??

cleaning the throttle housing and items is a good thing as suggested by Nathan3306 too.

 

Parts stores can't scan the old EEC system. You can do it yourself with a paperclip, there's a procedure around here somewhere for doing that, you will have MUCH better luck posting in the pre-1997 forum.

 

Yeah, I didn't know there was a pre 1997 forum, I have searched all over looking for someone to test this beast, not finding anyone who still does them, I don't think its a vac leak, or dirty fuel injectors, I have "cleaned it out" to the point of almost blowing the motor and there is absolutely no change, the other thing I forgot to mention is pre to this happening it did over heat as the radiator crapped out, I replaced radiator temp runs normal except when sitting with the AC on..