Another idea: check the pipe running to the throttle body for cracks, missing breather line, looses clamps etc. What you described sounds excactly like a boost leak on a MAF car.
IF there is nothing obviously loose, you can try a boost test. If you can build boost in neutral, have someone watch underneath the hood while you build 3-5 psi, then let off the throttle hard. The pressurized air will come out the void, and will be easy to see/hear.
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