A lean condition could create a few issues from lack of power to hesitation or surge upon acceleration. This is most likely caused by a vacuum leak, faulty MAF sensor, or incorrect fuel pressure. Since it's easy enough, check your fuel pressure and inspect your fuel filter to make sure it's not clogged. Check your vacuum lines for leaks. Vacuum leaks on the intake side can also cause the rpm to fluctuate.
Also, the A33 Maxima has had some known issues the upper plenum gasket not sealing properly creating a leak that could cause a lean condition. If you've recently installed intake spacers, you might want to check for leaks first. You should also inspect the MAF sensor. A dirty or faulty MAF sensor, possibly caused by an over-oiled filter, can cause the engine to run lean in one or both banks. Clean it with some carb cleaner and reset the ECU. If you have no power and can't rev higher than 2500 rpm, you probably have a blown MAF.
