My high mileage daily driver failed badly. Almost double the NO allowed. Here are the gory details: 15mph @ 1520rpm: %CO2=14.40 %O2=0.47 HC=44 (max 110) CO=.01 (max 0.72) NO=1476 (max 772) 25mph @ 1152rpm: %CO2=14.37 %O2=0.57 HC=35 (max 85) CO=.01 (max 0.59) NO=1051 (max 711) The service tech said it could be the egr, so I drove home and put a vacuum pump to the egr port. The engine stumbled as expected when vacuum was applied. That's about all I know to do to test the egr. I guess that doesn't prove that the electronic controller box is working. I think it could be the cat. 220k on this stock one; way past its service life. Before I start throwing parts at the problem, I thought I'd check here first. Besides the stuff in the signature, here are some other details: Scott Keller blue top smog chip, air filter and system returned to stock for test, stock (rebuilt) MAF used for the test, CA crap fuel plus some Heet and plus a little injector cleaner still left in the tank. I cleaned the top end with some Seafoam Green about a week ago and blew a lot of smoke out the tail pipe. New plugs and a fresh oil change before the test.