My 99 malibu stalls and is knocking faster
It idles the louder it taps. on 1999 Chevrolet Malibu

It will start and stall after few mins idling. Sounds like a tapping the higher it idles the faster it taps and I saw puff white smoke come from the valve cover as it stalled. Was thinking bad valve cover gasket and oil on spark plugs. Has been very reliable car until just recently. Now stalls sometimes when it's put into gear. Not sure what to start with!

Start by having a mechanic listen to the engine!!