IT'S NOT LEAN
NOx is from high combustion temp. The exhaust gas in the intake lowers combustion temp.
The exhaust gas comes from two ports near the #2,3 cylinders. A header or a wrong gasket could block those ports.
Is the test at idle or on a dyno?
I'm out of town so I can't compare to my 22RE, but it's possible that the vacuum directly to the EGR won't cause rough running/dying.
Can anybody with a 22RE test this?