Hi, fellas. New guy here.
This old truck of mine is giving me fits.
'89 F350. 7.5L ZF 5 speed 4x4 crew cab
It has almost 200000 miles now, and for the first time since I've had it, it isnt running well. I have had it for 23 years, and over 100000 miles.

It all started with an occasional stall when it would idle down after some highway time. It would drop down to 500 rpms, then stumble a bit. Sometimes it would stall and sometimes it would smooth out. I was too busy moving to mess with it then, so of course it got worse. It has progressed until now it won't continue running under 1000 rpm. Just to get it home, I zip-tied a 1/2" nut under the idle adjustment screw.

The first thing I tried was to unbolt the EGR valve. I stuck a wire in the big passage into the manifold, but didn't feel anything blocked. So I sprayed some emissions parts cleaner around in there and put it back on. Then I did the same with the IAC valve. That didn't have any effect, so I bought a new IAC valve from autozone and installed it. No change.
The cap and rotor were old and suspect, so I changed them. The wires are very new. No change. The spark plugs have 11000 miles, are gapped right, and look light gray. Almost white. Maybe too lean.
I'm stumped.

If you have any suggestions, I'd appreciate them.
For now, the truck is sitting in my yard taking time off, and I've been reduced to pulling an old beater trailer behind my wife's Subaru. I've lately had urges to leave behind my Carharts and start wearing Birkenstocks!
Help!

Thanks for your wisdom.
Bert

 

Man. I was sure hoping somebody would be able to steer me in the right direction here. Sorta miss driving the truck.
anybody?
happy new year.
Bert

 

start by pulling the codes and posting them up. that should the step 1 anytime you have a problem.

 

Yes pull codes to try and get a better idea before throwing money at it.

I had a low idle problem with stalling and also surging/missing when starting from a stop light.

I replaced IAC no change, got a lean code and replaced O2 sensor no change, checked fuel pressure and it was good, and then I was lost. So since surging/missing was a symptom of a bad MAP sensor (low idle is not normally a symptom of bad MAP) I replaced it and that was the problem.

Pull codes and check fuel pressure.