Pretty sure I found the main issue which seems to be a short in one of the harnesses going to the ECU. Looks like someone had done some work there. While I have the van running, if I move the harness in question just a bit, I can hear one of the VSV valves click, and the motor bogs down / dies. Hopefully redoing these wires will fix the main problem, don't know if it is the also the cause of error 4 and 11. Picking up a new multimeter to test the ECU and sensors.