Go to Autozone. Rent (for free) their fuel pressure tester. Easy to use.

Measure FP. Spray propane, or ether around base of manifold.

If pressure isn't 34-39 (steady) and if idle is affected by the manifold test, you've found the source of the problem.

Negative on the above two, and it may be the TPS. A simple volt/ohm meter will show if TPS sensors aren't consistent.