Recently noticing engine idling near 400 rpm,where it's rough & noisy. When dep[ressing gas slightly & bring revs to 650 -700 it's smooth & quiet. Is there a dial (like in older 300 D) to adjust idle ? If not please advise of idle sensor / actuator location to check connections & if working. Awhile ago I replaced glow plugs, & thought of possibility 1 of 2-3 hoses came loose & could cause lower speed. Thanks

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06 CDI diesel fitter
96 E 300 D (sold but still chuggin)
87 300d (sold)
87 300TD (sold)
01 ML 320 (what was I thinkin?)