Why Car jerking when idle

SOURCE: car jerks when brakes are applied

Highly possible that the rotors are warped. You may need to get them cut and replace the brakes.

SOURCE: car jerks while taking off; changed fuel filter

i have a 2004 pt cruiser and i put gas in it about 5 months it had trash in it and jerrked, i put gas treament init ran better. i changed where i get gas at well 5 monhs down the road it started jerrking again and gas trament help a little but the jerrking comes and goes like one day the car will runand the next it acts up...

SOURCE: 2003 hyundai santa fe constantly jerks while idling.

it has to do with the injection system. Might be something stupid like a manifold intake gasket leak (commonly known as cylinder 4 misfire problem) or it could be a part of the system like : spark plugs, wiring, fuel injector, throttle position sensor. A low cost solution worth trying is a kleen flow injection system cleaner. It will remove a lot of carbon and see if it helps...

SOURCE: jerking brakes

have the disc rotors checked for warpage and bad wear. Check that the wheel bearings are in good condition and properly adjusted. Check pad thickness as you may have metal on metal.