Disconnect the negative battery cable for about 2 mins and then reconnect.

 

do you have an old fashioned timing lite? I have a dwell tach as well but that wont help you in this case
unhook the coolant sensor (driver front corner of intake on that one) with it running that puts it into "set timing" mode then, set timing like your old cars and reconnect sensor then shut off and clear code as above
kinda (but not quite) like what happens with the old cars by disconnecting vac advance when you pull the plug on that coolant sensor

 

Okay, disconnect negative cable for 2 minutes. check
Unhook coolant sensor.. gotta figure out exactly what that is. anyway yes, I do have an old style timing light.

 

The 89 does not have a crank position sensor, the timing is adjustable. make sure the timing is adjusted to 10 degrees before top dead center with the coolant sensor unplugged.
The hall effect is created within the distributor, it increases the 12 volts to the plugs. if the hall effect was bad it would miss, this seems to bog down at operating temp.
the only thing i can think of is the EGR valve, mine went bad and it started no problem but when it warmed up it seemed like it was flooding (old time carbs).

 

I have seen many of these dist pickups start acting screwy once engine warms up.... and early on in the post, he had a Code 11 which says " no distributor reference signal" which would be.... the distributor pickup
Im not sayin that's the only problem that may be happenin with the OP's truck but it is(was) definitely A problem in this case.
I mentioned setting timing a few posts above a process the OP should be familiar with considering some of the cars he's had (and has said he has worked on while he owned)
the difference here being disconnecting an electronic sensor (coolant temp) instead of disconnecting a vacuum line from the vac advance can
but otherwise the actual "setting of the timing" process is the same.

 

Okay, cleared the pcm(?) by disconnecting the negative battery connection for 2 minutes. Started it up and it won't idle, lol. Runs high, then the rpms drop. Probably because things have changed and it needs to be re timed. Which I will attempt, but first, the coolant temp sensor, it's on the engine block between the valve cover and where the hose goes from the radiator to the engine, correct? Oval shaped, plugs in vertically?
I wish there were pictures online to see stuff like this.

 

You have to give the PCM time to relearn the settings. Start the engine, let it idle and come up to operating temp then switch it off and restart. The idle rpm should stabilize.

You are correct on the temp sensor.

 

By the way (raining here, and I'm waiting to know specifically if I have the coolant temp sensor located), there's a peep hole I have to time the engine to on this engine, right? It's there, and I've seen reference to it elsewhere. Just get the mark dead center, I guess? I have yet to see the usual notches and grooves that show the gradations denoting degrees before and after tdc.

I appreciate you all hopping in here helping. I swear, I've had so much trouble finding information online on the simplest things regarding this truck. My old '73 Baja Bug was a cinch to find information on back when I had it. You guys are a big help, thanks a lot!

 

Excellent! Looks like we posted at the same time. Will I need to reset the pcm again, or just hold my foot on the accelerator?

 

Just let it warm up, but a funny thing is happening now. The temp gage on the dash shows cold when the engine's running, but when I turn the ignition off, it jumps up to less than half way across. Odd.

anyway, it still won't stay running, it starts at a high rpm and idles for a minute, then dies.

On a good note, though, I did the three turns of the ignition to get codes, and it's down now to just

12
and
55

Father in law still says it's the computer.

I just came in to get some tools to go time it, and thought I'd post an update.