TomK [MA][99 BW 5.9L FT4WD]
tek@acm.org
It tends to get gunked up and cause idling problems. I don't remember where the inlet side of it is (maybe someone will chime in), but if you can spray carb cleaner into the inlet at idle (carefully, so as not to stall the engine) you can probably clean it out to some extent.
Beware: though it seems completely strange, idle problems on these D's are often due to a "dead" battery. It seems to have something to do with the regulaiton of the +12 line, and not with cranking power.. So.. that might be something to consider.
... tom