gaftop1

94 c1500 auto 4.3 idling fine then check engine light will come on and idle will go up to around 1200 rpm sometimes 1500 rpm. remove neg batt cable and reset. sometimes will be ok for a day, sometimes will do it again after a minute of idle.

unplug tps. voltage between black and grey wire is 5.0 volts replug and voltage between battery and blue wire is .75v idle, open throttle is 4.5v.
with truck running and meter on batt ground and blue wire idling will be .75v then volts will drop to .01v or 02v and code will set idle will go up. let it sit for 10 minutes start and may run ok may not.

changed the iac and tps now leaning pretty hard to ecm going out.
HELP!!!!!!!!

EinST

The only way the TPS output will go from ".75v then volts will drop to .01v or 02v" is if there's sudden drop in the reference voltage across terminals A and B. Before investing in a new ECM, I'd trace/inspect the wiring. Make sure there's nothing funny going on inside the electrical connector and splice in new wires when in doubt. I think the TPS wiring on yours looks like:

Terminal A, GRY wire, 5V Ref, from ECM connector C215, terminal F14
Terminal B, BLK wire, Sens ground, from ECM connector C218, terminal B3
Terminal C, DK BLU wire, TPS Sens, to ECM connector C218, terminal A15

gaftop1

went through the wire loom didn't break it open but don't see any pinches or breaks in the shroud. at the ecm don't see any breaks or pinches or rubs. replugged ecm, idle blue wire voltage is now .62 instead of .75v. grey remains at 5v. need some kind of fittings to check continuity don't want to keep punching holes in the wires. ordering a new tps plug just in case.

gaftop1

did continuity check on all 3 wires and they all check good. new tps, new iac, reasonably new egr
less than 5 seconds after starting the truck get code 22 light and idle goes to 1500 trans shifts at 2500.
leaning farther to new ecu. any other thoughts??????

EinST

I assume you checked the continuity on each wire and checked for shorts between wires and to the chassis ground? I'm fresh out of ideas, then. It does sound like a circuit fault inside the ECM.

gaftop1

well turned out it was the ecm. changed the eprom and all back to normal. thanx all

EinST

Congrats. Thanks for the update.