Have you done any work to it recently? How many miles are on the car?
Stab in the dark: It's starving for air. Open the airbox, check for a rat's nest. Make sure the throttlebody is not obstructed. Make sure there's nothing touching the wires inside the MAF sensor tube (the cylinder attached to the air box after the corrugated rubber tube on the throttlebody). Once saw the same thing from a feather stuck to the MAF sensor.