I also was not understanding the trouble correctly due to the way the post was written.
Like VDCdriver stated, the brake system uses vacuum air, which comes from the throttle body, to assist the power brakes and the brake booster most likely has an air leak in it, which will cause the engine to have trouble running correctly.
It might be a good thing that he paid a high price for the switch. Hopefully it will be a lesson for him to listen to others that have more knowledge about things than he does.