I have a 1999 mustang gt. When I press the brakes and the car is in neutral, the car will drop RPMS and stall. Sometimes even when the car is sitting the RPMS will drop really low and then rev back up. The car has a check engine light, and the code reads that it is running lean, and my brake light is also on. I replaced the IAC, EGR. I’m thinking there might be a vacuum leak but I searched for it and couldn’t find one.