Hi!..recently replaced the O2 sensor in the '93 245......with 240k on it, i figured it was about time..dunno what the p.o. had done, but i've put 110k on it in 3 years......had been noticing some valve noise, or pinging?, when going up hills and not great performance on hills...(and although it defies logic, it feels like i'm driving uphill about 75% of the time), anyway, since changing out the sensor, no more valve noise....even went back to 87 octane....and performance is better...and on the first long trip it looks like 1-2 mpg increase......not 100% clear on how these things are related but it semms to make sense if the system was having lean/rich issues....so..if you haven't changed yours recently, and i think the bosch website recommends 60k miles.....might help, if you have some similar issues......j.