Ugh,

Ok so I was finally able to both borrow a timing light and get some time to actually dig into this issue. Timing appears to be ~20° BTDC regardless of whether the "Engine Check Connector" is jumped or not.

Consistent with my internal logic, I did things in reverse order of what Tim suggested and eventually learned that *mysteriously* the clamps on the throttle body side of the air intake hose were loose and thus not air tight. However, there was no change in timing after tightening everything down and verifying (with brake clean) that the hose was air tight. Van appears to run fine (at least no worse than before this all happened), but it's practically billowing smoke out the exhaust now.

The TPS has been replaced somewhat recently (under my stewardship and per Tim's TPS video) but it is an aftermarket unit. I haven't touched the ECU since purchase, is that the next likely point to test?

Thanks again!

- Perry