Q: Car vibrates and tachometer indicator goes up and down

Idle fluctuation can be caused by a number of things. A vacuum leak can be one cause. If there is a broken or disconnect vacuum line, broken air intake hose, or gasket leak, the engine can draw in too much air. This effects the air/fuel mixture and can cause a surging idle or even stalling. Low fuel pressure can also be a cause. Either a weak fuel pump or fuel pressure regulator, or even a clogged fuel filter can cause this. Other causes can be one of the numerous sensors the engine control unit relies on for information. If for example, the coolant temperature sensor is not giving the ecu correct information on engine temperature, this can effect the air/fuel mixture and cause an erratic idle. Since any of these components can cause a poor idle, have a certified technician look into the causes to find the exact one.