1990 80 Quattro Problems

[Turse, Thomas (CORP, GEAccess)]

Okay, seems like the new car is finally coming together-  tires, struts,
shifter linkage, and broken sub-frame bolts replaced.  A couple of minor
things I'm trying to work out:

Anything to check for poor gas mileage- seems to be getting less mpg than my
4000Q?

Also, could a malfunctioning O2 sensor cause a funny smell and intermittent
erratic idle?

Finally, has anyone used Torque Master spark plugs?

TIA,

Thomas
Denver, CO