Pretty much as described -- the TPS (flat connector) signals the ECU that you're looking for idle, the IAC is the ECU's way to adjust bypass airflow (idle air amounts) and on automatics the NSS provides an "in gear" signal to the ECU to allow it to more aggressively control the idle speed.
One thing to look at for the TPS is that (if you're an automatic) the TPS will have qty=2 outputs -- the service books all talk about setting the TPS connector's values (the square one) in ratios as you describe, but don't suggest that you look at the other conector (the output to the ECU) assuming that they're both gonna fail at the same time...
... History indicates that the ECU's side of those dual TPSs fails quite regularly...
If you can't get your "ratio" settings to set-up - that usually indicates a bad TPS anyways which should be replaced.
Usually I recommmend loking at the output availabl on pin "C" of the flat connector (the ECU data) - it should rest at/near 0.8v with respect to ground (aka pin "B" of that connector) at idle and change smoothely to no less than 4.5Vdc at WOT.
Any "dirty" response (lack of "smooth") should warrant replacement -- similarly dirty output from the TCU (Tranny Control Unit = square connector) side should also warrant replacement.
Auto trannis should definitely be set by the TCU connector, with the additional step of verifying smooth operation and approximate V-out at idle on the ECU connector (IMHO, of course).
A thorough cleaning of the IAC and it's passages can help as well...
on that vintage, it's not too uncommon to have a vacuum leak in the MAP sensor's connection to the TB... Verify that you do not have that problem -- that'll mess-up mixtures all across the board (more at high-vaccum idle then at WOT) and impact your idle stability -
You may be looking at a mechanical issue with the TB and linkage as well (old springs and crud accumulation)
