Unusual emissions problem.... High NOx and O2

I recently failed my state emissions test. I drive a 91 Toyota Camry with 190k miles. Here are my results

High Speed (25mph)

Pollutant Standard Current Reading Result

HC (ppm) 123

26 Pass CO (%) .69 .
13 Pass CO2 (% ) 14.6 O2 (%) 19.7 NOx (ppm) 878
1093 Fail

Low Speed (15 mph)

HC (ppm) 128

127 Pass CO (%) ,71 .
31 Pass CO2 (%) 14.4 O2 (%) 20.4 NOx (ppm) 970
947 Pass

As you can see from the results, I failed on the NOx and was very close to failing on HC at low speeds. What particularly puzzled me was the high O2 readings. I looked at the results of my tests for the past 5 years and I have never had an O2 reading over 1%. What is going on here? Was it a malfunction of the test??

I should also mention that before taking the test I did all of the usual things to prepare for the test:

1. spark plugs have less than 2 k miles on them
2. changed oil and filter
3. changed air filter
4. checked spark plug wires and distributor cap for leaks
5. checked egr valve for proper functioning
6. checked compression. 170 - 175 psi on all cylinders.
7. drove the car for 15 minutes on freeway. Left the car idling before test.

I would appreciate a few thoughts about this problem. Thanks.