What do I do if my tachometer continues to rise when the car is in neutral. It is a 1998 Saturn

Have the idle air control valve and throttle position sensor checked-

The first thing I would check is the short hose that runs from the intake manifold to the pcv in the valve cover. They rott out and colaspe cause issues.I would also check the coolant temp sensor and the connector going to it. They fail often and cause idle issues driviabilty issues all kinds of things.