isolate the engine from all pneumatic accessories like vacuum diaphragms, brake booster, vacuum solenoid, evap canister etc.
connect a scan tool to the OBD port and read the fuel trims while engine idles, you should be seeing near to 0 long term and 3 or 5% short trims. If you had a leak and just did this - you will see the trims going down (meaning ECU is adjusting back to normal)
if you still see a problem in the fuel trims then do a smoke test (find a charsee freind or a cigar smoker and get him to blow smoke into the air intake manifold and then look for the leak) - sometimes a leak is not discovered by carb cleaner.
Some cars have a vacuum pod in the airbox which is used for air management. There can be a leak there - thats why its best to isolate everything and then test - if everything returns to normal then connect the vacuum users one by one and see which one messes the trims.
btw - if you pinch the brake booster you should not see any difference in idle quality if the booster is airtight, if the engine stumbles that means that you just cut off air supply and the ECU will slowly adjust it back, thats why I mentioned to connect a scan tool to your car and repair.