my 1997 z24 over revs when i push in the clutch in, what could it be? on 1997 Chevrolet Cavalier

it's 2.4L 5 speed manual, was making a chugging sound when idling so i replaced the spark plugs, now it is over revving whenever the clutch in and revs anywhere from 4000 to 6000 rpms. As soon as the clutch is released the rpm drops.