Glad you're making progress.

Idle up at 1,000 confirms your suspicion that the idle stop screw isn't properly adjusted and the plate is a bit too open, either that or the IAC has an issue. To confirm it's not the IAC, do like I said and rap on it while running to see if the idle immediately drops down to normal. A slight drop in idle is semi-normal for an older TPS, but a drop of like 100 rpm is a sign of a sticky/dirty/worn IAC.

You said you were using an old writeup to adjust the throttle body. If it wasn't one of my writeups and talks about using the idle stop screw to adjust base idle to a set rpm with the IAC forced closed then that's old thinking from the LH 2.2 days. The preferred method for LH 2.4 (and LH 3.1) is the 1/4 turn method I mentioned (it's in the later and superseding Volvo tech bulletin I have on LH 2.4 throttle adjustment specs and was confirmed some years ago by a Volvo Vista Master Tech here). Ideally this is done on the bench, but you can do it on the car. With the linkage rod disconnected and the TPS loose, loosen the nut and back off the idle stop screw. Now with your fingers inside the throat holding the plate firmly closed, advance the stop screw until it touches and to the point it's just about to start moving the plate, then advance 1/4 turn more and secure the lock nut (followed by that drop of paint as the security marker I mentioned, nail polish even liquid whiteout works fine).

Now properly adjust the TPS. From my old notes which were based on the Volvo TP bulletin. "Adjusting the TPS: It should trip just as the throttle moves away from its stop so that the ECU knows when it’s no longer supposed to be controlling idle –you’ll hear a click and a click again on the return. You don’t want the TPS click adjusted right on the hairy edge, it needs a bit of tolerance. For optimal adjustment as determined by Volvo, proceed as follows. Start with the switch rotated clockwise away from the stop position. For a Bosch switch, hold the throttle plate closed, turn the switch counter-clockwise until it clicks then continue to the end of travel and lock in place. For a VDO switch, insert a .010" feeler gauge at the idle stop screw (if you don't have a suitable feeler gauge substitute two strips of medium heavy bond 24 lb. computer paper), turn the switch slowly counter-clockwise until the click is heard then lock in place."

Also, having to re-center the throttle pate is a sign the shaft may be worn in the bushing, usually the spring side, allowing unmetered air intake. Do a leak check as I mentioned.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now