I think you may have a fuel gel problem. the temp at which B100 gels is dependent on what it is made from. most b100 is made from soy in the US, which shouldnt gel until 32 deg F, but maybe your bio cam from a different source and has a small percentage of something else that gels higher. wvo soy also gels higher, or so i am told.

the fuel pump is pulling on the lines for fuel, which are blocked upstream due to gel, and thats where the vacuum is coming from.

dd

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car