GearHead_1
Long Time Member
When I made comments last night I had not known all that had been done to your van. Knowing what I do at this point I would think your issues are either EGR system, a vacuum leak or electrical. That leaves you with only about a million possible scenarios. It's easy to block an EGR valve of for testing purposes. A can of quick starting fluid (Ether) can be used to find the majority of external vacuum leaks, internal is a different story. Basically it's get it running, rev it slightly and point the ether at the gasket surfaces or potential air leak places making sure you're not shooting it directly towards the air inlet. Leaving the intake system hooked up helps keep the inlet isolated from the area you are working. If the RPM's change dramatically (you've in essence added a second fuel source to a lean condition) you'll spot the leak.
Since you've had the intake manifold off and worked on the throttle body these are good places to look for a vacuum leak. You can still pull a plug wire at a time and find out which cylinder is not contributing. This lets you focus on the air path of that cylinder should it be vacuum related. Don't forget to look at the little vacuum trees and all vacuum lines attached to the trees on the intake runners as well as the power booster vacuum source. I'll bet you can run this down.
Since you've had the intake manifold off and worked on the throttle body these are good places to look for a vacuum leak. You can still pull a plug wire at a time and find out which cylinder is not contributing. This lets you focus on the air path of that cylinder should it be vacuum related. Don't forget to look at the little vacuum trees and all vacuum lines attached to the trees on the intake runners as well as the power booster vacuum source. I'll bet you can run this down.