The linkage is free and clear. The throttle completely closes each time. The decel switch is new because it was working intermittently and it is working perfectly. Throttle Position Sensor is working properly; always 0 ohms between pin 1-2 when throttle is closed.
Even though all these items are working properly, the car still fails the test (short pins 1-2 on TPS, 2500 RPM, press decel switch & engine should "hunt"). After flooring the accelerator briefly, the car then passes this test.
Flooring the accelerator for an instant ALWAYS "fixes" it. Idle cutoff works perfectly after that. At least until next time you drive the car.