Smog Problems On Sc400

[plutnium]

I just recently purchased a 92' sc400 at an auction and I am having problems getting it to pass smog. The %CO2, %O2, HC(ppm) and CO(%) passed with flying colors, but the "NO(ppm)" failed in the gross polluter range (ouch). Max is 757 at 15mph and mine got measured 2641!!! At 25mph the max is 696 and mine measured 2898!!!! (double ouch!!!) I already got it a tune-up, oil change and removed the egr valve and cleaned it out(the top port going into the egr valve was completely blocked). I did this before I did the smog test. Is there a way to test the egr valve to make sure that it is still functioning properly? Does anyone have any ideas on what it might be. It seems to run clean, no smoke out of the exhaust and runs smoothly, everytime I go back to the mechanic they say something else needs to be changed out. I fear that I will have to replace every sensor and part by the time they get done with me. Any help would be appreciated. I am just looking to get it to pass smog for now. I can change things out here and there later as money comes in.