idling problem 525tds
hi everyone,new to this forum! just wondering if any one could help me with a problem! i have a1997 e39 525tds automatic,that is idling at round 600rpm, the funny thing is it doesn't conk out,it drives fine when i up the revs! does any one have an idea what could be wrong,i'm no mechanic so fire away, every little helps! thanks!