Unless you can find one of these from another 164 / 1800ES / 1800S or 144 with Bosch D-Jet fuel injection, they are I believe no longer available 'new'.
The idea is that the Aux Air Valve automatically adjusts the amount of air drawn into the air intake as the engine warms up, according to the engine temp. Once the engine is fully warmed up the aux air valve is no longer needed. The problem is that they gradually seize up, and then stop working. It only becomes a problem in colder weather, and can I think prevent the engine from idling.
Brookhouse Volvo here in the UK certainly used to sell a kit which gives manual control over the aux air inlet. Basically, rather than rely on the automatic function of the aux air valve (which is controlled by the temperature of the coolant), the driver has a manual control that worked like a choke works on a carburetted car. I should imagine it would take a bit of getting used to, but no more than driving an older car does anyway.
I can't see anything on the Brookhouse website today, but it would certainly be worth dropping them an email or a quick telephone call.
Cheers
Jack
PS. If I remember rightly it is possible to adapt the equivalent part from a 240 with the B21 engine? Not 100% sure on that, but I think I remember reading this somewhere.
PPS. I see that Brookhouse now do a reconditioned exchange unit:
http://www.classicvolvoparts.co.uk/p...ID=39&scID=280