Drew, your issue also sounds like the IAC valve, which is on the rear of the intake manifold. It is what that weird plastic contraption attaches to that connects to the rubber hose connector at the throttle body. They are not super expensive. Outside chance it is just a vacuum leak.
The exhaust rattle is likely a bad catalytic converter. It has disintegrated to the point of only having one piece honeycomb left that is bouncing around inside it. More of a nuisance than anything as I doubt you have emissions testing for a car that old.
97 T-Bird LX 4.6 - 80k miles
94 Supra TT Auto - street/strip car
04 CVPI- Brenda's car - 76k miles
95 T-Bird LX 4.6 - fully optioned, owned 15 years, 220k miles
96 Cougar XR-7 4.6- Brenda's car, owned 11 years, 187k miles
88 T-Bird 3.8 - first T-Bird, owned 5 years, 206k miles