Tbanks, Doc. That confirms my suspicion. The TDC sensor on the torsional balancer does not appear to be adjustable, and I could find no other way to change the initial timing.
Being as how my HC is high in the first test (15 MPH) on the CA ASM emission test, I was hoping to retard the timing a few degrees to increase the EGT. The exhaust manfolds only read about 470F with an IR gun near the head interface after several minutes of idling. I was surprised they were so cool with only 9 degrees ignition advance at idle. I suspect the converter is cooling off after several minutes of idling, which gets me near the limit on HC until the converter heats up. The HC on the second test - 25 MPH - is much lower relative to the limit, but still above average for my year group.
My most recent test a couple of months ago yielded 113 PPM HC at 15 MPH, and it did not help that they lowered the limit to 116 from 141 two years before. In that prior test I intentionally went in on a rainy day and asked them to run the "tire dry procedure" where they operate the engine at about 25 MPH on the rollers with no load for about a minute, then go right into the 15 MPH test. The HC was 87 PPM, and the O2 content was zero. In this last test with 113 PPM HC there was 0.1 percent O2, so a hotter converter will promote the use of that last bit of O2 to oxide the HC and CO. The O2 content for the 25 MPH test was zero in both the most recent test and two years ago. For my next test in a couple of years, I'll go on a rainy day again!
My '88 190E 2.6 has been identified as a "high emitter profile", and this may apply to other models with the 103 engine. There was a lady ahead of me in a '91 300SE and she made the 15 MPH HC bogey by only 1 PPM!