Failed emissions, but what needs to be fixed?

[rojo412]

My 91 ES250 is rating high up there on one of the worst buying decisions I've ever made, even though it has taught me so much. That aside, it failed Ohio's E Check miserably and I don't know why. I got it waived, but would still like to fix it (if it is running silly rich, that costs me money). So to the experts, here goes:

The testing concluded that my NO levels are more than quadruple the legal limit (read 3387 ppm, passing is 848 ppm). My HC was a little high (136.7/120), but either way it failed. Any clues as to what needs to be done? I don't want to put more into this than I have to because I want the car to go away, but still have to use it.

What you have to know (maybe): The speedo doesn't work, EGR was eliminated, and the cat back was replaced 3 years ago. The cruise was also eliminated, some vacuum lines have been taken away, but the car starts and runs exteremely well.

[Doctor J]

What is the O2 level??
Vacuum leak and misfire + plugged EGR valve causes high NO under load and high HC on idle
When I first tested my car it failed at 2000 ppm NOx.
Fixed by setting timing, changed spark plug wires cleaning the egr system, fixing the air leak

[rojo412]

I have replaced the plugs, cap and wires. I just finished the timing belt/water pump job and had it set correctly... I guess? I think I may have to have that looked at, though, now that you mention it. Where was your air leak, btw?

It doesn't tell me O2 level and I don't have a way to test it at home here. I assumed it could be a bad O2 sensor and at $43 it isn't terrible difficult to do, but I don't want to throw it away if I don't have to.