I'm posting this as a new thread, because I think I figured out why I was getting the 70% fixed duty cycle on my California model 1991 190e 2.3 and it is no longer the question.

Now, the reason for my interest in the duty cycle is that I failed Arizona emissions. My HC readings were 347 Loaded and 439 Idle, with both at a max allowable of 220. CO was 1.46 Loaded and 0.95 Idle with both at a max allowable of 1.20.

It seems that the car has always had a slightly audible misfire, so I was suspecting that was the cause. I bought the car two years ago and since then I've changed all the usual suspects like plug wires, cap and rotor, spark plugs, air filter, fuel filter along with regular oil changes. I even went so far as to change out the ignition coil, fuel injectors and seals, checked for vacuum leaks, etc. Everything as a whole helped the cars performance, but it still has that miss.. Finally, I just threw on a cheap cut and weld cat to get it to pass for the last couple years.

Anyway, I just did some lambda adjustments and here's what I came up with:
With the black/wht striped purge hose disconnected, (as recommended in the Landiss article) I can get it to run at ~50% duty cycle (all readings fluctuating) at idle and ~44% @ 2500 RPM. With the black/wht striped purge hose reconnected, I get ~45% duty cycle at idle and ~33% @ 2500 RPM.

My understanding from these readings is that it's trying to compensate for the rich condition at 2500 RPM (due to the misfire). Is that correct? I also now realize that I should have adjusted the idle duty cycle to +/- 10% of the reading at 2500 RPM. Instead, I adjusted the idle close to 50% and then took a reading at 2500 RPM. Still, that equates to +/- 10% of the reading at that the point where I had the purge hose disconnected.

Therefore, my question is, are my lambda settings as good as I'll get right now until I fix the miss? Or is it possible, that the miss might have something to do with my lambda adjustments? Also, should I try to get the duty cycle reading at 2500 RPM closer to 50%, with the "purge hose" connected?

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2000 c280 Sport (looks like an upgrade, feels like a downgrade)
1991 190e 2.3 (sold)