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Have you read faults on it? You can get them read for FREE at Autozone or other large parts stores if you don't have a scan tool of your own. It would save you from just throwing expensive parts at it. Let me know if you have fault codes and I will help you figure out what is the cause, and what codes are just peripheral because of the main fault.
In the meantime- have you listened for a vacuum leak, since the brake pedal is assisted by manifold vacuum? Try removing the oil cap with the engine running to see if there is a vacuum on the crankcase, indicating a failure in the PCV system
Are you able to read fuel trims short term and long term on your scanner?
Does it suck down hard? (if you put a piece of paper over it, would it suck flat, or does it pulse in and out) Or is there pressure pushing out?
Does it change the idle issue at all to have the oil cap off? If you pull the vacuum hose off the brake booster, is it pulling any vacuum at all? Check at the ports at the back of the intake manifold as well