I'd appreciate thoughts from the group on my test results:

Test 1: Friday Aug 12 (Failed due to faulty Check Engline Light)

MPH=15 RPM=1546 %CO2=14.9 %O2=0.1 HC(PPM)=43 CO(%)=.13 NOx(PPM) =762 Pass
MPH=25 RPM=1864 %CO2=14.9 %O2=0.1 HC(PPM)=21 CO(%)=.07 NOx(PPM)=648 Pass


Test 2: Monday Aug 15 (Fixed Check Engine Light)

MPH=15 RPM=1517 %CO2=15.6 %O2=0.0 HC(PPM)=41 CO(%)=.15 NOx(PPM) =948 FAIL
MPH=25 RPM=1714 %CO2=15.5 %O2=0.0 HC(PPM)=14 CO(%)=.06 NOx(PPM)=662 Pass

Any thoughts on where I should begin to source the problem. New 02 sensor and Bosch plugs were installed 3-weeks ago.

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Steven
1989 260E (276K miles)
1995 E320 (50K miles)