Revvs itself up for no reason

Failing transmission

For 90% of cars that try but just can't start. Key off, Pump Gas Pedal 4 x, holding it to floor (all the way down) on 4th time, then just turn key. as soon as engine starts and revvs up, let go of the gas pedal! Seriously... Do not keep the pedal down!!! This is b/c engine is 'cold', the oil that lubricates your precious engine is very thick, and you don't want to add other problems (scarred pistons/cylinders/rings and oil burning or a severely overrevved engine (screaming) at no load (you are not in gear - no drag of car weight on motor) resulting in major engine damage.

When does is rev high and low? If it does this at idle check for a vacuum leak or maybe a blocked airflow

that is your idle air control valve. it is located on the throttle body next to the throttle position sensor

Most likely a vacuum leak somewhere

Check the throttle position sensor and idle control.

I think you should buy repair manual first for your vehicle after that it will be easy for you to solve the problem. Check the link may be you will get something useful here 1988 Nissan 200SX

this is a computer controlled autobox.on a flat road put it into drive and without using the gas pedal let the car accelerate itself to max speed (about 35mph)then stop and do the same with only an inch of gas pedal.stop then gun it,put your foot hard down to the floor until you reach a speed that is just safe for the road conditions.
you have just reset the computer.....if you drive it gently for a few miles,you may feel a difference,if not then get it onto a diagnostic for a health check....

Sounds like the throttle position sensor It is attached to the throttle body up by the intake Go to the part stroe and get one if your not sure what it looks like

Throttle position sensor. It's under recall for most Malibu models.