Have a 1984 300SD w/188,000 miles and noticed my idle has been a little rough every now and then. Checked the rack bolt and realized it was almost all the way in. So I adjusted it out a ways and then started to turn it back in at half turn intervals till the idle smoothed out. Ended up turning the bolt almost to where it was to begin with to get to idle well.

Only thing is as I was turning in the bolt it seemed to have much better acceleration and overall performance but the idle suffered till it was returned to its original position. I now know I need the new updated bolt. I guess my question is does the Rack Bolt only affect idle quality or does it affect the whole range of performance and idle at the same time? Also where is the best place to buy a Bolt? Thanks for all your help.

What is your idle RPM? It might be a touch low, which causes rough idling too.

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I have it around 650-700 rpm's, so I dont think that is it.

Mine was about that and I had a somewhat rough idle. And on cold starts the rpm would cycle up and down but 50 rpm or so. I adjusted the idle to 750 or maybe a touch higher and it went away.

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I guess I am giong to ask a stupid question....... Where is this rack dampner bolt? Is it the idle speed set screw?? Is that adjustable??

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My Truck.. 2007 DODGE, 5.9 Cummins, 6spd stick, 4X4. My car..1977 240D, OTHER WHEELS...1955 VW Oval window bug, European Delivery (Holland) with a 1700cc, 2 barrel, Porsche drum brakes. 1939 WILLYS Pick-up. 1967 Triumph 200cc Tiger Cub. 1976 Honda 550F 4cyl Motor Cycle.

The rack damper bolt is on the rear of the injection pump. On the bottom. The idle speed screw is on the top of the injection pump inbetween the IP and the block.

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