Thank you guys for the for confirmation and reinforcement. I saw the van again today and did some more troubleshooting (new air filter, new fuel pressure regulator, check spark plugs, try to make sense of the vacuum lines).? When I got to removing the SAI, it was already disabled (a small plate blocking the metal pipe to engine head).? So all that fiddling with vacuum lines and valves was unnecessary, the system was dead anyway.
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So here is what I know at this point:
1. when the Fuel Pressure Regulator and the Atmospheric Pressure Sensor (in the ECU) vacuum line is connected, engine runs fine at first but eventually dies at idle.
2. it runs best with FPR and APS disconnected, the vacuum line open and sucking in air.
3. spark plugs are black and sooty.
4. oxygen sensor is probably dead, disconnecting it wouldn't make any difference.
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When I see the van again in a few days, my plan is:
1. change the O2 sensor,
2. change the fuel filter,
3. test the idle valve (it is vibrating to the touch with the key on, but have somewhere an old one I can swap in),
4. test the EGR valve
Anything else? Thanks a lot for your help!
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