rpms up and down from 700-400 what do I checkwh

Check for vacuum leaks, snug up the intake manifold, look for cracked vacuum hoses, and what controls the idle is the Idle Air Control Valve. Should take that out and clean with carburetor cleaner along with the port the valve goes into. Lube up the o-ring slightly when re-installing it, care must be taken. Clean the throttle body plate and throttle body also. Another thing to clean would be the Mass Air Flow Sensor, and the screen. Use the appropriate MAF cleaner, do not use carburetor cleaner.