Weird Idle (1988, 90)

[David Bokaie <David_Bokaie@NeTpower.com>]

Car is 1988, Audi 90, 5 speed, 115K


For past week I have noticed that when hot on de-accel such as coming to
a traffic light in Neutral, the engine speed drops to 1-1.3K rpm and stays 
there
for a while until it drops to its normal 800 rpm.   Also I believe that on
steady freeway  speed I can sense that engine rpm wants to fluctuate similar
to when cruise control is engaged.

Does this mean that the oxy sensor is going bad.  I did not see the voltage 
spec
for it in Bently manual.  Other suggestions?

Thanks,

David


ps:  I live in bay area/Calif and for the past couple of months I have 
notice that
my mileage has dropped from its normal 28-30 to 25-27.  Not sure if the
gas in this area has changed?