It's clear to me that your EGR valve is non-functional and needs to be replaced. It's critical to passing the NOx cutpoints.

Years ago my '88 190E 2.6 five-speed was getting marginal on HC, so I retarded the spark advance map by removing the R16/1, replacing it with a homemade shorting plug and blocking the vacuum advance line to the EZL module. This retards the spark advance map that increases EGT, making the catalyst more efficient, which reducers HC, and it also reduces peak combustion temperature that reduces engine out Nox. My model does not have EGR, and these mods also dramatically reduced NOx.

These temporary mods will probably get you a pass even with an inop EGR, but you should replace it.

BTW, removing the R16/1 resistor completely will dramatically improve low end torque/power and around town fuel economy due to the more aggressive spark advance map ,but probably won't pass emissions.

The following two threads provide more details. I have a background in emission control research from the U. of Wisconsin Engine Research Center back in the late sixties.

M103 Emission Test Insight

Successful CA ASM emission test (KE fuel system)

Duke

Tnx for the link, but it's a different one that won't fit the M103. The right one has only one fitting.

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

Passed with the new EGR valve.

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

Good news. Did you find new or good used as mentioned in your earlier post?

Would be nice to disassemble the old one to find the failure point and find a repair method. It's a common failure with parts NLA.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Found an almost new EGR valve sold by a Mercedes mechanic in Santa Monica.

The old one was completely toast, rust made it so weak it broke in pieces when I took it off.

One thing I noticed, I have less power from 0 to 30 mph with the new valve.

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).