1989 F-150 4x4/351 Windsor, fuel injected, 185,000 miles. Plugs, wires, rotor button, and rotor cap replaced a few months ago.
The engine started running rough about a week ago, when I first start it in the mornings it will stumble, try to pick up and stumble repeatedly having to keep it reved up to keep it from stalling, takes about ten minutes to get it to run good enough that I can get down the road. Doesn't seem to lose power or smoke like it's flooding. I have to put it in neutral at stop lights and keep it reved up to keep it running it's running so rough, no matter the distance driven when first started for the day it doesn't clear up until parked and driven later in the day.
Any other time of the day it runs some better, but it does stumble at random then run smooth again but it doesn't seem near as bad.
Any help appreciated! Thanks!

 

It may be your IAC. Try what is said for troubleshooting at the bottom of this page Ford Fuel Injection Idle Air Bypass (IAB).
Or now that I've found it https://www.ford-trucks.com/article/...r_IAC_Fix.html here is a better place to troubleshoot it.

 

Replaced that thing a year or so ago, $80 some dollars. Problem wasn't nearly as bad thru me a curve although it was the first thing I thought of a week ago but refused to beleive since it had been replaced.
Thanks for the quick response.

 

Thanks for the quick response. That's the first thing I thought of a week ago but I had replaced it a year or so ago so I wasn't sure if it would be bad again already, but the link you gave me explains the problem I'm having exactly.

 

do a compression check i am having this same proble in my 93 brono and i lost the #8 cylinder

 

I cleaned the Idle air control valve today put it back on and tested it by pulling the electrical plugin to it, results were the same as before cleaning, the truck stalled out when the electrical plugin was removed so I guess it is working correctly from what I've read here.
I noticed a little flat 3 or 4 wire sensor of some type up under the bottom of the throttle body under the two big air hoses that mount to the front of the throttle body where the IAC mounts, every time I moved the electrical plugin to it the engine would either speed up or spudder could that cause the problem?
The other thing I noticed is that there is a vaccum hose with some sort of little cyclinder in the air line that fastens to the front of the throttle body when the electrical is pulled nothing changes but when the vaccum line is pulled from the front of the throttle body the engine reacts instantly.
I'm lost, fuel injected vehicles are beyond me, too many sensors!

Thanks for your help!

 

That would be you throttle position sensor. They are 40 some odd dollars and really easy to replace.

 

Thanks for the reply!

 

Correction: Price was $60 some dollars for the Idle Air Control Valve instead of $80 some dollars as mentioned earlier.

 

I would check to see if you have any stored codes. If you don`t have a code reader look at the top line of this forum page and click on "Tech Info" and then on OBD1 for instructions on pulling codes without a code reader.

 

This is a valve for the fuel vapor return system, it only opens when you are decelerating.

Pull the codes and see what is happening with the truck. Also, did you install the IAC in the proper direction, as the old one? I have always seen the selinoid end of the IAC towards the upper intake.

Are you saying the throttle position sensor moves when you wiggle it, or that when you mess with the wiring to it that it works. Either your TPS is loose or the wiring has a short in it for the TPS.

 

The cyclinder end of the IAC is towards the front of the truck on my engine.

The wires your asking about go to a little flat plate that fastens up under the throttle body under the two big air hoses, if I move the wires around the engine will idle a little rough at times, not every time, if I leave it alone it runs smooth.

 

Thanks Lazy K. I'll have to check into learning how to check the codes.

 

I would definitely check the codes for any errors but moving the wires on the TPS, the little metal place below the throttle body, should not effect the idle quality of the truck. You may have a broken wire in the TPS or a bad connection in the harness or the wires leading to the TPS, maybe even a loose TPS.

 

I replaced the IAC today and the engine still ran pretty rough, although I beleive it helped some, I'll let you know tommorrow after I swap back to the old one and try it against the new one.
Later while removing a spark plug I struck a corregated sheath with my hand and it slide back enough I could see a white plastic vaccum line that had been broken for a long time and another one that looked as though it had just recently broken. I repaired 2 of the 3 vaccum lines that were in the sheath and so far the engine is running smooth again. The plastic vaccum lines that were broken came from some sort of can mounted to the passenger side frame. Thanks again for all the help!