i was wondering how to adjust my idle speed on my 85 300td. for some reason when it reaches operating temp it seems to stay at around 1000rpm and even sometimes 1100rpm and its getting on my nerves because it is kinda loud just idling at that high of an engine speed.. is there a way to adjust the idle speed without using a data link connector and a scanner?

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1985 mercedes benz 300D turbo diesel
1998 VW GTI VR6
1996 VW GTI 2.0
1999 saab 9-3 turbo
1987 300sdl (sold)