ACDelco, I guess. I'm not sure I'd be that gung ho about assuming and throwing parts at it, though. Chances are, there may be one or more wiring problems. Good luck.

 

Reset the codes and the P0300 as well as the O2 sensor codes came back. No TPS yet. An O2 sensor is only $35, much easier than troubleshooting a possible wiring issue. If there's still problems then we can explore that route. If I'm not mistaken when there's an O2 sensor issue the computer just richens up the mixture to prevent engine damage correct? Which would cause the post cat O2 sensor to appear bad? That's my thinking at least. Start with the pre-cat first and go from there. Why the P0300 I'm not sure. It shouldn't run that bad with a bad O2 sensor I'd imagine.

 

P420/P0430 is almost always a defective catalytic converter. I still think what I wrote in my post #7 holds.

 

Well, I was finally able to take the van for a test drive myself and it was running horribly. Felt like it was missing and running on 6-7 cylinders and the CEL kept blinking. I went ahead and changed the TPS and the bank2 precat O2 sensor as the codes suggested. The van has run perfectly ever since. The CEL did come back on with a P0430. I've told him to drive it for a few days and if it doesn't clear up we could try replacing the post cat O2 sensor as well and if still not luck the cat eventually. But for the time being the van is running much better which is the important part.