1985 vanagon1.9liter sluggish gas mileage is terrible

disconnect catalytic wires coming from exaust chances are you no longer have to do emissions check its more than 20 Yrs old

Facing the engine on the left near the exhaust are 2 thermo switches replace those switches and be sure not to cross the wires. If the wires have previously been off at the same time it may be as simple as swapping them back to there designated switch.