What is this foil covered piece?

[azfabguy]

You must be registered for see images attach

 

[hogdaddy]

ESC Vacuum Switch.
On LE9 engine equipped vehicles with automatic transmission a "tip in" vacuum switch is used. Its function is to provide a momentary contact closure (signal) to the ESC controller during a throttle "tip in" condition which then briefly retards spark timing to minimize knock. The switch contacts are normally open under steady engine vacuum conditions including no vacuum, and all brief increasing vacuum conditions. Basically the switch closes only during rapidly decreasing vacuum conditions such as that encountered on rapid throttle operation.