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There are about 25 possible places for an intake air leak. most are not easy to spot. Start by checking your gas cap and oil filler cap for cracks, bad o-rings or obsolete part #s. Get it up on a lift and inspect your oil filler tube for cracks and AOS bellows. Re-trace your steps when the throttle body was removed to make sure nothing was overlooked or knocked loose during the process. Inspect all the little vacuum lines for cracks/leaks. It is there somewhere. Some guys use a little propane around all the intake fittings with the motor running. If you hear an increase in revs it will indicate a leak location. As you know propane is pretty flammable and I have been seared by a propane flash fire before so it is not my method of choice but it does work.

The good news is that an intake air leak is usually an inexpensive fix if you DIY. It just takes time and patience to track it down. Good luck!