Sean,

Low miles is irrelevant to the throttle switch issue, they get dirty when new or old, contact is lost and drivability issues result. Cleaning the throttle switch is simply maintainance. Check the vacuum pump diaphram if so equipped, they tear causing a significant vacuum leak. All new vacuum hoses are in order on these cars, 25 years is a long time for rubber exposed to oil and gas, and as you say, leaks cause problems.

The smoke is white, correct? Sounds like a transmission leak. The BW-35 has several items to leak on the starboard side including a plug near the top of the case, the cooling lines are right over the exhaust.

The BW-35 is an ok transmission, they last if over maintained, frequent fluid changes and band adjustments and throttle cable adjustment is critical. No vacuum modulator for controling shifts. Borg Warner sold this same unit to Internatinoal Harvester for use in Light Line Scouts, Pickups and Travelalls, those units are still working. The Volvo units have a bad rap, I think due to comparissons to Big 3 car units which are more docile. Synthetic fluid can do wonders for the longgevity.

Good Luck