VT relearns the TPS at ignition on
VN- does not at any time
I went back to the engine management workshop manuals for a couple of models using the 1227808 to be sure I wasn't misremembering something. In the TPS output check and under the two fault codes for the TPS is: "The TPS is not adjustable. The ECM uses the reading at idle as "0% throttle", so no adjustment is necessary."
From a VT series mass air flow manual: "The PCM will learn what the closed throttle value is every time the throttle comes back to closed throttle.". I can't say with the same certainty what VR and VS do but they should do what VN/VP and VT do respectively. GM is not lone in non-adjustable TPS, self-learning ECM either.
The learning makes sense as, apart from manufacturing variation between TPS's and throttle bodies, base idle speed adjustment will alter the TPS signal voltage at idle. I suspect the learning each time the throttle is closed, as distinct from only on key on/start, is to avoid stalling caused by intermittent sticking of the throttle varying the apparent base idle speed and the corresponding IAC motor steps needed to reach the desired idle speed prior to feedback correction.
Fair comment re. having the revs above 2000rpm for long enough for the IAC valve to close. I still say just drive the car.
Interestingly, in looking up the TPS info., I also found that an IAC reset can also be forced on the 1227808 (VN-VP) by inserting a 10k ohm resistor across terminals 'A' and 'B' on the ALDL connector. These are the same terminals that are shorted with a jumper wire to extract the codes by flashing the check engine light on the dash - a 10k ohm resistance is what Tech 1 uses to indicate to the ECM that it is connected to the ALDL. The > 2000rpm bit is still required.
