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I believe I wrote that note about pinching off the hose. It's a quick roadside test you can do to check IAC functioning and was recommended by one of the Volvo masters tech over in the ALT.AUTOS.VOLVO discussion group. The biggest danger in doing this is splitting an old hose. Wrap a rag around the hose before squeezing it with pliers. Disconnecting the line and putting stoppers in both ends is another approach.
If your IAC is really sticking (and it may well be, especially if it's the older 3-wire type and you haven't been overly religious about cleaning your flame trap and intake hoses) then grounding the service wire may not cause the valve to fully close. If that was the case then you'd not be setting base idle at the proper point. If clamping the hose off causes the base idle to drop much more than about 25 rpm below what the grounded wire method achieves than I would say it's time to haul out, clean and possibly replace the IAC. Even when seemingly clean, the older 3-wire valves have a tendency for the contacts to wear grooves in the motor's commutator that can lead to erratic movement and sticking of the valve.
There are two minor problems in setting the base idle point lower than the 700-750 rpm spec (auto-manual). First, when the accelerator is released from higher rpms and the IAC valve slams shut, the engine may go a bit lower than the target 850-900 rpm idle for a brief moment before it bounces up to normal. Apart from hesitation and possible stalling when cold, this might also set the CHECK engine light on OBD equipped cars. Second, if you set it too low then the top end of the open range may not be enough to produce a suitably high cold idle under extreme running conditions -such as temperature extremes and extra loads such as using the A/C for defrosting and having the alternator flat out feeding headlights and heating accessories. Please note that the rpm's I've stated here are off the top of my head as an example, so check the spec for your particular engine.
Having said all that, if your goal is just to set base idle then I'd ground the IAC test wire and solidly tap the IAC motor a few times to help make sure it's fully closed. But first I'd do a thorough throttle body clean including cleaning out every hose, orifice and pinhole and removing the base idle adjust screw and cleaning/blowing out its passageways. If tapping on the IAC motor makes any difference in idle rpm then the motor is getting sticky or you've got a loose electrical connection.
-Dave
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