I realize this is about 5 years since the last post in this thread, but Richk5 posted one of the best explanations of the problem I've seen. They are not all exactly the same though, but to say it's likely a broken wire when this problem rears its head would be a pretty safe bet.
Mine turned out to be a wire broken. 6 inches out of the ECM, it rubbed the frame until it wore through the insulation. Then it corroded. Then it caused too much resistance in that circuit and burned out part of the ECM Board.
I had looked into the TPS, cleaned all of it. Start it and get 0 volts to the top two wires that run the throttle body MOTOR. So, I assumed one of those two wires was broken. Stripped it all the way back to the ECM and all 8 wires coming from the throttle body to the ECM are good. Wiggle-test and tug-test good. So, I'm a little miffed and upset at this moment, because I was hoping to find the smoking gun.
I decided to open the ECM just because. I figured that was the cause now, since there was *some* response to the pedal (so it's likely not the APS in the pedal), the motor in the TBA worked, if I applied external voltage to it. The wiring was ok. So, it HAS to be the ECM, right?
Inside the ECM, I find a layer of smoke on the case, and some burnt parts on the board. Bingo. Smoking gun. I'm done. (If you think that, you've probably burnt out good parts chasing down the bad ones.) I know that I'm not really DONE, I need to find out WHY the board burnt.
The burn marks were right where the main board has the long feeder probes to the harness connections. Which connection was it? I sort that out by counting them from left to right... #9, top, on the red harness. Where does that wire go? I better chase that down. It's red with a green stripe. So is this one. And this one. And another. Damn there's a lot of those here. They kind of go in this mess and out there, so pull back and forth on both ends until you find the one that matches the pull.... oops, one just came out of the bundle. Corroded wire, worn insulation. Looks like the one that I was pulling on, but it's not. It goes to the pin above the burnt one. Where did that rub? Oh look, right there on the fender. NOW I have a smoking gun. Soldered in a new stretch of wire (I even put a FUSE in there, just in case). Back to the burnt terminal... it goes up to near the engine block and... wait for it... is spliced with the broken one and several others. What? Why do that? That makes no sense Isuzu/Honda/GMC. Oh well, we're now ready for a new ECM.
Photos to come in another post.
And the results of a "new" ECM install. (no way I'm paying over $1000 for an ECM for a car that's worth <$1000)