um i shook it and some shakes inside of it and egr in on top of the vaule cover right but the funnie thing is that lik were the hissen comen frm lik it louder on top but wen u go underneath the car it quiter it realli hard to find it i felt every weres i change the thei ntake manifold i sprayed carbotarotr clean n the throttle body clean dat it like were is that hissen comen frm
idlen bad on 1999 Mazda 626
The item on top of the valve cover is likely to be the Positive Crankcase Ventilation Valve (PCV valve) it can cause a hissing sound if it it defective or the hose going to it from the intake manifold is leaking. Disconnect the hose attached to the PCV valve and with the engine running put you finger over the hose does the hissing go away and the engine idle more smoothly.
The EGR is not in or on top of the valve cover. It is an electronic device that has a connector. it should be on your intake manifold.