this car has 134000 miles. runs great, the only issue is the car shakes terribly at idle especially with the ac on. the car is idled at 850 rpms. intake is cleaned. iac valve cleaned. no check engine light. fuel injectors were cleaned. plugs and wires are new. vaccum lines are good. and the car has kind of a knock to it thats not a motor knock but instead happens very slowly as idle goes up. its most prevalent around 1800 rpms. car has a low whistle coming from one of the pulleys and the pulley coming from the crank rocks ever so slightly back and forth. could this be a harmonic balancer issue?