I can't make any sense out of your software version number. All my tests going back to the beginning of ASM testing are yy/mm format. I've never seen a software version number that has only three digits. My 190's last test early this year reported "0.0%" on both the 15 and 25 MPH tests (as did the MR2 last week), but I don't know if the system rounds off or only reports 0.1% when that level is reached. In any event, reporting O2 to two decimal places gives a better indication of how well the catalyst is performing.

Was this a "test only" station, and were you directed to a test only station on your registration renewal?

I use a test only station a few miles away from me in Manhattan Beach. When I brought in the MR2 in last week, two or the three bays were in use and one was open, so I got right in with minimum idle time. There was one car finishing up when the Merc was tested in February. While waiting I keep the AC on Max with the windows open and hold revs at 1500 to keep the catalyst as hot as possible with some load. Minimizing idle/wait time is critical to keeping the catalyst bed hot, and shutting the engine down is a big no-no.

The tech remembered me as the guy with the stick shift six-cylinder Mercedes from early this year.

How many miles does your '90 Accord have, and how does its reported emissions compare to your Merc?

For my '88 model year, Mercedes recommended changing the O2 sensor once only at 60K miles. Mine appeared to function okay at that point, (and still does) so I didn't change it, and the bienniel (soon to be annual if AB 616 passes through the legislature, which it probably will) gives it a health check.

That device on your exhaust manifold is an EGR valve. My '88 doesn't have EGR, (or an air pump), but NOx is still low and VERY low with a retarded timing map.

Duke