So I've noticed that while my 88 pickup idles high frequently, it will drop back down to something that sounds much more healthy with a quick blip of the throttle, which makes me wonder if adjusting the speed screw would help at all.
I also have occasional momentary flashing of the engine light, which a couple times has actually stayed on until I shut the engine off and then stayed off for a while (weeks). I read the codes, 13, 51, and 71, and see what they indicate in the manual. Seems like a lot of ˟˟˟˟. Given that the codes are still there, even if the light is not on all the time, I'm guessing there are still some issues. I don't really know where to start though.

 

Sometimes the throttle Linkage gets crappy... spray some WD40 on the springs , cable, and bushings.

 

First thing to do is clear old codes. Easiest, pull the negative lead off the battery for more than 1 minute.

THEN, once you get a CEL, read out the code(s). Otherwise, if you don't clear the old codes, you could be reading codes from a previous problem, or three. The ECU stores the codes.

Let us know what codes you get THEN. That way we know they are for the current trouble. And, as stated,WD-40 on the throttle linkages, springs etc on the TB may solve the entire troule. They do get sticky. Get the WD-40 with white lithium grease mixed in. It lasts a lot longer.

Good luck!
Pat☺