1996 BMW Z3 Smog Failure - California

Passed the following:

Visual
Functional
CO2
O2
HC
CO
(I tested extremely low for all of the above).

I failed NO (PPM):

15 mph (1982 RPM): 459 (allowed) 1065 (tested)
25 mph (1997 RPM): 746 (allowed) 278 (tested)

My first thought was cats, but the disparity between tested scores vs. Tested RPM has me thinking something else. O2? ECV?

Thanks in advance for the input.

By the way, drove on the freeway at 3500 rpm for an hour prior to the test.
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