Not sure how to "prove" it, but it is fairly common for the better platinum or split-fire plugs to not work well in some engines due to the location and angle of the plug within the combustion chamber. That will not cause the engine to stall which is what I think you mean by "powering down". Those better plugs will typically cause misfires that you often can't even feel but will be detected by the Engine Computer.
The first mechanic tried to sell you higher-quality parts than what came as original equipment. You're lucky the problem was just the wrong spark plugs. If you are angry that they tried to provide better service, the best thing you can do is never go back there.
Tuesday, May 10th, 2011 AT 11:49 PM