I've got a 1989 F150 with the 5.0. When I first start it, it doesn't matter if it's cold or has been running for hours and shut off, then immediately restarted, won't idle unless I give it gas for 2-3 minutes. It jumps from 500 rpm to 1200 rpm then dies, or almost dies, then repeats unless I press the gas and hold it at around 1200.
I do have a CEL which I checked and it shows codes 51 and 84. One is the EGR vacuum solonoid and the other is the ECT sensor.

I do plan on addressing these issues, but I'm wondering if either of these could cause the idle problem that I'm having? I have cleaned the IAC, tested the TPS, new fuel filter, ran Seafoam through it, good fuel pressure on the rail.

Any thought or ideas would be awesome!

 

Start by fixing those codes. Chances are they have something to do with it, even if they don't cause it they should be addressed. Once those are gone and stay gone then if you still have the idle problem start looking for the cause.

 

I don't disagree, as I said, I am going to fix those problems, I was just more curious than anything if those would cause the idle problem.
Thanks for the insight.

 

Both will cause the to run bad. I would fix the ect first. Ur ect is dumping to much fuel and flooding the engine. Sounds like the plugs need to be cleaned also.

 

Replaced both the EGR Vacuum Solonoid and the ECT sensor yesterday. No CEL now and she starts right up and idles perfectly! Thanks for the help! I'll check the plugs next because I don't know how long it's been running this way.