95 SL2 DOHC NOx failure

My 95 SL2 (DOHC, 215k miles) just failed the Harris Co, TX emissions
test for the second time, NOx in both cases.
After the first failure I replaced the EGR valve, which was pretty
dirty and which may have been sticking. I would occasionally get the
32 error code, so the computer thought there was a problem with it
also.
I also replaced a number of other items: coolant and air temp sensors;
plugs; plug wires; valve cover gasket (old one leaked oil into the
spark plug wells, no reason to put new plug wires into pools of oil);
air filter. Changed coolant; changed oil and filter. Also cleaned out
the throttle body and idle air control valve. Also replaced the PCV
valve.
Second time around it also failed, at least the first part of the test
- high rpm on "dynamometer" test, NOx failure as before.

I would appreciate any repair suggestions that will get this thing to
pass. Most of the parts I've replaced fall into the "routine
maintenance" category, but I don't want to continue down the "try
replacing this" trail unless there's a good chance that it'll solve the
problem. The blue book value on the car isn't that great, and since I
anticipate moving outside the Harris Co. air emission testing zone in
several months it'll be a moot point anyway.

TIA.

Bob T.

 

Sounds similar to my failure two years ago with a 93 SL2. I failed four
years ago, but cleaning the EGR valve made it pass. Two years ago I
replaced the EGR with a new one, as well as the EGR solenoid, but no dice.
Under a broke people's assistance program, a garage changed my catalytic
converter for a few hundred, and that did the trick.