Fuel Injection system

did you check the O2 sensors and your vacum lines

I just picked my Nissan Maxima 2000 from the dealer. It had a similar problem - the engine stumbled during acceleration and I was not able to rev it above 3000 rpm. Before going to the dealer, I changed the spark plugs but that did not help. Then a computer diagnostic indicated an improper fuel/air ratio. After a mechanic friend of mine said there could be three culprits: the throttle position sensor, the mass flow sensor and the EGR valve. Unfortunately he lacks the specialized equipment required to tell exactly which of these parts is broken, so I took it to the dealer. The dealer replaced the throttle position sensor and the mass flow sensor and now the car drives like new. Therefore I suggest you check these three parts. If you can get used parts for your car ask a local mechanic to replace all three. If you cannot get used parts, it is probably cheaper to take your car to a dealer or a shop specializing in Japanese cars. I hope this helps