Check valve for brake booster? (Automatic)
 

I currently don't have a check valve for my brake booster in my automatic car. Is this dangerous or is this something I could leave off my car? Could not having a check valve in brake booster cause a lean condition? Should I just pop it back in?

I believe it’s there so that if your engine stalls, you still have a few power-assisted brake pedal applications before totally losing brake assist. Leaving it out is a bit of a liability.