I have a 1989 F-150 with the 5.0L engine with fuel injection. Lately I've noticed that sometimes when I first start the truck, it'll run for a bit, then cut off. If I keep my foot on the gas, it'll keep running. If I start it again, it'll idle fine. Sometimes when I first put it in gear, it'll stall out. Again, if I restart the truck and put it in gear, it'll run fine. A couple of times when I was stopped somewhere, it idled very low, around 500 rpm, and acted like it was about to stall out. If I start moving again then stop, it seemed like it idled a bit higher, around 700-800 rpm.

Also, if I turn the air conditioning or defrost on if the truck is in Park or Neutral, the truck will stall out. However, the air conditioning and defrost work fine while the truck is in gear.

Any ideas on what I can check out?

 

Loose distributor? Maybe try turning it a little until it idles around 850-900 rpms.

 

Thanks Peacemaker, I'll check it out tomorrow.

Any other suggestions or ideas out there?

 

Are you sure you have TBI on an 89 5L?
The last year for TBI was 84 into 85 then full fuel injection started.
Normally a dirty IAC and dirty throttle body will cause your type of problem.
The computer has to control the bypass air to control idle. If this doesn't work well the idle does not either.

 

Oops. Not sure why I said TBI..

I think the IAC was actually replaced before I bought it, but that doesn't mean it couldn't be dirty. What's the best way to go about cleaning the throttle body?

 

Ok, so I took what I'm thinking is some sort of solenoid off of the front of the IAC. I cleaned up the inside of the solenoid a little bit, then replaced it. I started the truck and turned the A/C on and it actually kept running. It was idling between 500-700 rpm. I tried it a few more times, a couple of times it would cut off, but other times it would continue running. Once or twice it would act like it was going to cut off, then surge back and forth between 100-1000 rpm.

The friend I'm buying it from said the IAC was replaced, but I'm thinking that they may have just replaced the solenoid, rather than the whole thing.

Any thoughts?

 

Take the whole part off at the two mounting bolts.
Get throttle body cleaner and clean until it comes out clean.
Do the same to the throttlr body while holding the throttle full open spraying all around inside past the throttle plate.
Re install and see what you have.
The computer needs some drive time to re adjust it's program to any different operations.
The inside of the IAC has a pintel valve that the attached solenoid moves to vary the air bypass, This must move without sticking or hunting occurrs.
There could always be other problems but address these first.
Do not adjust the throttle stop at this time.

 

Thanks Bluegrass. I'll try it out and report back what happens.