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The IACV on the Regina system controls the air flow to the intake manifold when the throttle plate is closed. This contols the engine idle RPM. The IACV is a solenoid plunger valve (unlike the rotary valve in the Bosch LH system). That part you saw moving back and forth was the plunger valve. I don't know how far it is supposed to move but, if it is moving freely, it is probably OK. The resistance you measured, 4 ohms, is the correct resistance.
The idle speed is controlled by the ECU, there is NO manual setting. The ECU can be confused several ways. I'd check the following:
1. check very carefully for any possible vacuum leaks
2. check the operation of the idle position switch using an ohmmeter, not just listen for the click at closed and open throttle. I use some very small clip leads from Radio Shack to connect the ohmmeter to the switch while I operate the switch.
3. check the postion of the throttle plate in the closed throttle position. The PO of my '93 940 had tried to set the idle speed by loosening and adjusting the throttle plate. He only made the hunting idle worse. I had to use feeler guages to get it back right.
4. check to see if the O2 sensor is working
5. clean and tighten all electrical grounds you can find
6. there was a TSB about half way through the '93 model year from Volvo telling the dealers to open up all electrical connectors (except the O2 sensor)
spray a contact cleaner into the connectors, apply some silicone grease, and reconnect.
I've done all the above and the hunting idle is gone. Also, if you've disconnected the battery, the ECU has lost its memory. The ECU will have to relearn its best settings through several drives. During that time the idle can be unstable. Good luck, it took me awhile to get mine to stop hunting and I'm glad I spent the time.
One last thing, if the idle dips too much when the AC comes on, there is a TSB fix on that.
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