why would car idle go up and down

Bevauae ur amf sensor needs cleaned or replace. Coroded wireing harness mb manufactre fault so replacement of harness is nesisary also preventing more problems... Relay fuse shot. Coils or spark plugs may need replaced or cleaned. Filter oil and maintenence maybe required. Also may be a fuel or air blockage.

It may help to clean the idle control valve. This is an electric motor controlled by the engine control unit restricting or allowing air running in a hose from the crankcase to the inlet and fuel delivery body.