If you feel lucky... you might want to look at this.
http://www.rangerovers.net/discoparts/
I copied this from that site. Sorry, not sure I could get the link to work even if I tried.
*****If you are interested in experimenting a bit, cheaper alternatives can be tried, at considerably lower cost than the genuine part or those sold by the traditional Rover aftermarket suppliers. Salvador, of Baja Rovers, Mexico, found that as we suspected the idle air bypass valve/stepper motor is indeed a GM part #25527077. He found the Napa part number is 2-1738. Phil Tetzlaff reports finding this part at his Boulder Colorado NAPA store, but later exchanged it for one manufactured by AC Delco, part number 217-437. It appeared to be of higher quality (in casting density and spring strength) than the Napa brand part, and indeed appeared to be exactly the same as the Land Rover part. The final kicker was that while the "genuine" Land Rover part is well over $150, the Napa part cost was $51.99, and the AC Delco only $38.51!" (However, prices have gone up considerably since then due to the fall in the dollar). Greg Olma suggests “Go to a junkyard and take your pick from GM 4 and 6cyl. I use PB'laster to clean em.” Richard Atkinson reports that this is perhaps the most popular GM idle air motor, and is eqiivalent to AC Delco part number 73312A, He says it also crosses to AC 17085051, 17086051 and 1717111288, amongst others, which were fitted to almost all 3.1L V6 from '90 - 95, '85 - '86 2.8L V6, as fitted to Cavalier and Celebrity, '85 -'92 5.0L and 5.7L V8 Camaro, etc. etc.
I have recently done more research into this mysterious part. Searching the NAPA parts directory, I did not find this genuine AC-Delco part, but they had an equivalent off-brand "Mileage Plus Fuel Idle Air Control Valve" part number MPF31738 for about $40 at Napaonline.com. (Glenn Coffman went to NAPA recently (June 2004) and they gave him a P/N 2-1736 for his 91 RR for $57). I found they had an alternative matching Echlin part number CRB21738 for $52.99 (a better known brand). I also discovered that the GM Part number 25527077 is the AC-Delco part number 217-437. Various internet GM parts sources sell it for around $50.
The lowest price I have found recently (November 2003) was at AutoPartsGIANT.com for $36.58!! (search for fuel injection parts, 1989 Chevy Astro V6 -- subcategory idle speed control parts).
Update July 2004: Cory Novak found that partsamerica.com & sister store Advance Auto have the Idle Air Bypass Valve for $27.99 in stock most of the time it is GP Sorensen 779-10003 & item number 5012678.********
