My 98 Golf GL failed the emissions test last weekend because the check engine light was on with OBD code P1582, which apparently means 'Idle adaptation at limit, clean throttle housing'. Now, there is some history to this. I had the engine control light on for most of the past 2 years. The car has seen the shop 3 times already. First it was diagnosed with a vacuum leak and I had 2 hoses replaced, then they replaced the breather valve and (allegedly) cleaned the throttle body. I was told the last time that if that does not fix it I would need a new throttle housing, which is like a $500+ job including the parts. The light was off for 1 trip or so, after that it was on again. Sometimes, at less then 1% of the time, it is off. The car runs fine, even with the AC on, and gas consumption is normal. I don't want to spend that much money for unneeded repairs. What can I do to make sure that they will actually solve the problem? What can I do myself to try to diagnose the cause or even fix it?
Thanks in advance. c at donners dot com