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Hi Warren,
Well as I rely on my car I finally caved in wne to my local Volvo dealer parts department and bought a new throttle body, opened the bonnet in dealers carpark and swapped them over, then went to the service department and gave them the keys to get the unit reprogrammed and thus saved a chunk of money in labour costs (hows that for cheek!). If you know what you are doing the changeover only takes 20 minutes and requires no more tools than a 10mm 1/4 drive socket and ratchet, a 2" extension and a screwdriver. Much better than the 2 hours Volvo wanted to charge!
As for the throttle body, I stripped mine down to the nth degree over the weekend before I caved in. Internally there is a shaft running full length of the casing, two end covers, each with a throttle position rheostat (more on this later), a spring and a throttle position motor.
Each rheostat has two tracks with a common wiper. The wiper design in my opinion is poor as the end of the wiper is bent 90 degrees to the rest of the wiper but towards the resistant material, thereby acting as a scraper. This is I think the problem. Over time the carbon resist material gets scraped away by the wiper until the resistance is erratic, thus causing the ECU signal to be confusing and causing the TCM to shut down. The question is, is it possible to get the resistant material resprayed on?
If I get time and inclination I'll pull apart the old TCM and photo it to show what I mean and how to disassemble / reassemble it for cleaning (cleaning fixed it initially for about 15000 miles). I'll also have a chat to the guys at BBA and compare notes with them...
Alastair
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