You've sort of checked everything separately, but it sounds like you have not checked it as a complete unit. First, the two pins the you jumpered on the TPS that made a difference are the ones for idle mode. If the idle switch is (A) good (B) properly adjusted (C) throttle linkage is not holding it off idle, then simply watching the timing marks while connecting/disconnecting the TPS plug will show a change. If it passes that test... all that other checking, adjusting, testing is not needed. By not checking as a system, you have not eliminated A or C.

Sort of like getting out a voltmeter, ohmeter and whatever else to indivially test light bulbs, switches and wiring. If you turn the light switch on and the bulbs light, there's no need to check parts of the system.

If you confirm that the injection system is in idle mode (TPS circuit closed) and the timing is still 12 deg (assuming that you have not touched it since the e-test), then the test centre's pickup probe must have been misplaced.