Last night I started up the car to do the vacuum leak test and the engine stumbled a bit and almost stalled out and notice the check engine light on. New codes! P2279 Intake Air System Leak and P0507 Idle Control System RPM Higher Than Expected. Petrified.rabbit I can already sense your head shaking at me lol.. This is the first time these codes came up. I continued with the propane torch on all the vacuum lines and wouldn't you know it there was no change in RPM! It did accelerate on it own tho. I thought I found a leak but the engine stayed at that RPM and didn't come down. I went over a few more times over the PCV hose, the two small vacuum hoses and the booster hose. No change or fluctuations in RPM. I'll try it again this evening when I get home. As for the brake booster this was replaced for the same problem I've been having. This was replaced back in April and bought at the Chevy dealership AC Delco brand. Of course the problem continued as it did with the old booster. This later was led by the replacement of the master cylinder. Again, same problem and symptoms. Master cylinder was diagnosed by the tech at the dealership who said that was the issue. Of course it was not and even purge the system twice for air. The problem that this car has been having is sudden loss of braking power. Like as if the booster didn't have vacuum or something. The brake pedal would go stiff and your need extra effort to stop. But it doesn't always happen. It's random and no real pattern to it other than it used to happen in the mornings when you start the car. After driving about a block braking works like always and quick to stop. I drove the car for a week and it never happened to me except for once when I was backing out of the drive way and the pedal got stiff for a 2 seconds and returned back to normal braking. Even the tech at the dealership could not replicate the issue even after leaving the car sitting in the lot all day. But with these new codes we are getting closer I hope.