The key is to make sure that the vacuum is getting into the system in enough volume. I have seen where there was enough vacuum when the gauge was on, but not enough volume. the little filter for the vacuum system was partially clogged. It is about two inches from the pump and is clear plastic.
The disableing of the EGR and Intake valve will work as you mentioned.
1992 500E (very soon I hope
1981 280GE SWB
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