Low speed HC seems to be a problem with the 103 engines. I'm marginal in my latest CA "acceleration simulation mode test" scoring 113 ppm against a limit of 116 at 15 MPH, and it didn't help that they lowered the limit from 141 in the previous test a little over two years ago. The 25 MPH HC is much lower relative to the standard.

Converter temperature appears to be an issue, so driving the car to thoroughly warm it up and not shutting it down prior to the test is important.

Do you know the history of your O2 sensor? I have a suspicion that they can "drift" without giving a check engine light. My current plan in two years is to have my '88 190E 2.6 tested, and if it fails, just throw a new O2 sensor in it and see if that helps. The converter system is very expensive, so you want to exhaust all other possible causes before replacing the converters.

You should also search the board under "emissions","O2 sensor" and "duty cycle" as you will learn how to test the behavior of your O2 sensor, and I would recommend just replacing the O2 sensor apriori if the duty cycle is out of spec before you attempt adjusting the air flow meter as an O2 sensor that has drifted out of calibration will affect the duty cycle while not sending a properly calibrated signal, which could cause a rich or lean condition.

Your limits are higher than in CA, and I assumne your state uses a different test. What state are you in and what is the test procedure? I/M 240?

I'd also like you to post your complete test results - HC, CO, NOx, O2, and COx and the standards/averages for each test if all of this data is available on your test report as it is in CA. Looking at the entire results can help diagnosis. For example, high HC and low CO can indicate excessive misfires, which points to the direction of ignition system commponents such as the cap, rotor, plugs, or wires.

Duke