Why is it that my 4.1 motor on my cadillac fleetwood idles more when i press on the brake?
Because when you press on the brake, which has a vacuum operated diaphragm, vacuum is supplied to the diaphragm and pulls the idle down slightly.
My idle goes up the car was not doing that before brake booster is aftermarket
I believe your mechanic is right about this being brake booster related. There's a vacuum leak allowing additional air into the intake when the brake pedal is pressed which causes the engine speed to increase. One possibility is the brake booster diaphragm leaks air when the pedal is pressed. Is your aftermarket booster rebuilt or new? Another possibility is the check valve or vacuum hose has failed between the booster and intake manifold. You might be able to hear hissing start & stop from under the dash or hood when the brake pedal is pressed and released, revealing the source of the leak. If not, there are several other ways to check for vacuum leaks. Look at some of Scotty's videos on that subject. Good luck.
Yes the brake booster is aftermarket rebuilt i will checj it out thanks
No prob
How much higher does the idle go? Never heard of this before. This is till a function of vacuum changing in the engine.
This car so old so the dash does not tell me how much but you can hear it nothing crazy my mechanic says its the brake booster it only does it when i press the brake