What are the signs of plenum spacer air leak??

 

A hissing sound, erratic idle perhaps. You can check for a leak with propane. Run the propane around the perimeter of the plenum. If the engine speeds up, you've found a leak.

 

is that safe? lol

 

is it ok for me to do this, put silicone sealant around each bolts and around the plenum? I think i may have a leak.

 

Thats putting a bandaid on a sucking chest wound. Take it apart and find the reason for your leak.

 

i didnt install it, I just notice this now when decelleration at almost stop the rpm will drop to 1k rpm then goes up 1,200 rpm then back to 1k rpm then goes down slowly at idle rpm thats w/o stepping on the gas just brake until the car gets fully stopped. Im not sure if i have a leak, the rpm stays steady in place when idle at 750 rpm.