Just another data point... when my '85 failed emmisions (Portland Oregon) 
I hoped for a quick fix by replacing the O2 sensor. To my pleasant suprise 
it did fix the problem. I never noticed a MPG penalty before or after the 
replacement though.

Steve H

| Yes, the 02 sens light is designed to come on at certain 
| mileage 
| intervals and has to be reset on order to turn it off. Does 
| your van 
| run any different with the new sensor? My Mechanic 
| (PetroSillos 
| Bros.) told me not to bother getting a new one because they 
| don't 
| make any difference, ie, the control center can't even tell 
| if its 
| there. He said they were initially put on to control 
| emissions, but 
| he has tested buses before and after installing new sensors 
| and 
| couldn't notice any change. Let me know if you noticed any 
| improvement, in mpg or whatever.
| 
| Marc
| '84 Vanagon Wolfburg