So I am trying to get my 76 280Z running well so that I can drive her to school, but I cant figure out a real reason she keeps running this way. When I start to accelerate or even just push down the pedal while in neutral the rpms will drop and then start going up. As the rpms rise between 1000-2000 it will backfire in the intake. But as soon as it goes over about 2000 rpm it will speed up the way it is supposed to. It is also idling at about 700 rpm and it should be at 800 rpm. I heard that the reason for the backfiring could be because of bad gas or too low of octane rating. I am running cheap 85 or 86 octane from Maverick, but I just put in some octane boost to the remaining fuel, and I also just added a cold air intake with a K&N cone filter. So please if you have any idea what could be causing my car to sputter and then backfire out the intake I would be very thankful.