I am having the same problem with my 2000 Maxima! My check engine light came on in about 60K miles. so took my maxima to Torrance california dealer Its on Hawthorne Blvd. they tune-up my car put new sparkplug new belt clean the fuel injectors flush radiator and transmission and cost me $885 but light is still on so I talk to service person why my service light still on and he said you need to take your car where you bought it from.I'm still driving my with light on its now @ 80k miles. very poor gas mileage some times engine knocking and also engine vibrate on idle.
If it was a Nissan dealer, call the Nissan 1-800 number and ask them why these guys won't fix your car. I think you'll find that it's a bad O2 sensor or catalytic converter. The coils are a weak point as well. Good luck!