Ok so i just had the catalytic converter replaced day before yesterday, new brake pads a week before, and i have NEVER had this problem.....

I noticed since i have been driving it.......i go to stop....and my brake pedal takes awhile to kick in.....almost as if i can feel the presseure change and as i stop the engine almost stalls out......the harder i stop the more it wants to stall......when im pressing on the brake pedal, i can hear like a hiss noise and then i feel the brakes kick in but they dont kick in well. What the hell is going on? I havent bled the brakes in quite sometime and my buddy thinks its just air in the brake lines. But since its wanting to stall, i think it may be vacuum related or o2 sensor related? I have replaced the sensors closest to the headers......but the sensors before and after the cat have not been replaced.



Help!

 

No fluid leaks btw.......

 

Vacuum leak from the brake booster would be my first guess. Find the hiss, that sounds like your best starting point.

 

ditto the vacuum leak

 

Got it fixd......brake booster went out