What is YOUR car supposed to idle at?
The Cadillac and Monte Carlo are probably automatics, which probably idle slightly higher (1,000 rpm) than a manual (750 rpm).

So I don't think your problem is the idle, but rather a leak in the intake somewhere, so when you press the gas, air comes in unmeasured, which causes it to stumble.

Find a repair manual and start looking through it for the checking procedure.