This reminds me of damage done to electronic systems when welding is done in an industrial setting. You essentially were welding with your screwdriver as the rod. The dc voltage at the engine location would have been above the normal close to zero volts because of the amperage being sent through the engine block to the battery ground cable connection. This can cause juice to run through wires not intended to carry such large currents in a backwards directions. Also, the currents would have an abnormal waveform which could confuse the PCM and actually send corrupted data into the PCM through sensor wiring connected to the engine.

If the IPR is slow to act at low rpm, the feedback loop from the IPS to the PCM may overcompensate. The PCM reads the HPOP pressure at the ICP and the actual rpm. If the PCM sees that the requested rpm is not being met, the PCM will attempt to raise the rpm. But by then, the slow IPR is bumping up the rpm, at which point the PCM would see that and using the signal to the IPR try to lower the idle.

Like any control computer, the PCM has a programmed delay in the command programming to allow the engine to respond to it's commands and to allow the PCM to decide what to do next. If this file is corrupted by the "welding" you were doing, it is possible you are seeing the result of this.

It is also possible that the PCM is looking at the ICP values or the RPM values and comparing them to a corrupted file.

I forget-did you replace the PCM or have it tested? It might be worth sending it somewhere and having someone check it out, letting them know your symptoms. I am leaning strongly toward the PCM having a problem.

Did you run the warm engine without the belt?

Good luck,
Larry

 

I didn't swap the pcm, I don't have a spare and with snowplow season here I can't afford for the truck to be down at all to send it out. Wish someplace local did that. I didn't warm the truck without the belt. I could probably try that tommorrow. I need to put the first alternator back on anyways. Isn't it gonna die quickly without not alternator charging the batteries? Or am I just dense in this matter?

 

I forgot you swapped the alternator. No need to remove the belt now. You proved the alternator is not the problem.

 

Okay. Cool. Still want to swap back. I want to keep the newer one for the spare.

 

Don't forget, you still have your AC pump on there. Anything that spins can load up at some point and if it malfunctions.

When you're driving and noticing the trouble, is your AC turned OFF? Make sure the entire climate control is off.

Are you monitoring your system voltage when you notice the oddities?

They make little things that plug into the cigarette plug that are pretty inexpensive.

If there is a voltage change, you could have sudden loads it is reacting too...like ABS pumps, in-cab inverters, headlamps, etc.

These beasts aren't always easy or cooperative to troubleshoot

Still following along, hoping you find a smoking gun that is easy to resolve....