My 280zx seems to fluctuate in its idle. When the car is cold and in high idle it is smooth, but when it warms up the idle adjusts to about 800 RPM then drops to 500 and immediately rises back to 800 and then back to 500. It does this constantly up and down idle pattern. when it drops it sounds like it drops a cylinder for a second and then regains. Other than that the car runs excellent once I am in the throttle. Thanks for any help that you have.