So I've been hearing this hissing noise every time I press the brake pedal. I started to look into the issue and I thought it was the brake booster, and actually picked one up from a salvage yard. Problem is that the hissing is not coming from the booster, I narrowed it down to a switch. This switch is directly near the brake switch. It is a plunger type and moves just as the brake switch does when I press the brake pedal. However, there is a vacuum line that attaches to the back of it and it hisses when you press the pedal. I have pulled the vacuum line from the back of the switch and put my thumb over it and pressed the pedal, hissing stops. The vacuum line runs through the firewall and hooks into a T vacuum fitting that splits off to the engine block and the brake booster. I am lost, what is this switch and what does it do. Take a look at the picture for a closer look. Please help!

 

I was hoping someone would have gotten back to me by now, but I've just plugged the hose off so that I don't have to listen to it. I'm going to keep trying to figure out what this switch is and what it controls.

 

That is the vacuum release valve assembly for the cruise control which is used on the automatic transmission models.

I did a quick search on RockAuto.com, but could not locate a replacement for this part.

 

I have found a similar model part, but I think instead of just replacing it I'm going to remove it and disable the cruise control altogether. I don't feel the need for it right now, but at least if I decide to fix it later I will know what it is now. And I'm glad its only a control for the cruise instead of something more vital. Right now I'm going to focus on rebuilding my throttle body because I have a sticky accelerator problem.