Uncontrolled runaway and no throttle response are classic signs of an IP on its last legs. You get no throttle response when it goes runaway (won't idle down when you release the accelerator pedal) because the IP is mechanically seizing from wear and the stepper motor can't over come the resistance. I can't ever recall either the early series '94 APPS or the late series '94 APPS NOT setting a code when they go bad. The early '94's were upgraded to the later style APPS and the PROM reflashed/replaced with the updated program to work with the new style APPS on a factory recall (IF the owner brought it in). If the APPS was bad, it would have set a code for it.
Meanwhile, Will's suggestions should be undertaken. Yes, bad ground(s) can cause some crazy things to happen on these trucks. The clear fuel line is a great diagnostic tool and entrained air in the fuel can cause all sorts of idle/surging problems, too. But as somebody who has owned a late '94 since 2002 and over 220K miles and has replaced a couple of IP's that have worn out, as well as the ones on my 98, you are most likely looking at replacing the IP whether or not you want to accept that.
