Hey Im having a huge problem and have not found a clear solution. I have a 1970 mustang with a 302/4 barrel.

Just over a year ago I went through and had a complete brake job done on my car at midas where they replaced everything including the master cylinder. The car was in storage up until a few weeks ago and after giving the car a tuneup and putting a new carb on the car I noticed that the idle was having problems. The only time the idle has a problem is when the brake pedal is depressed all the way. So while sitting at a stop light it feels as though the car is about to stall... and the car actually did stall out sitting in my driveway in drive with the brake on.

If anyone knows the problem and how to fix it or has any idea of what could be going on I would be greatly appreciative. Thanks.

 

I believe your power brake booster has a leak causing the loss of vacuum to drop your idle down. There is a rubber diaphragm inside the booster and it is probably perforated and in need of a rebuild.

an easy way to check it is to disconnect the rubber hose at the booster and plug it with a screw or something. Run the engine and press your brake pedal to see what happens. If the idle is not affected, then you know the problem is in your booster.