My 1980 300SD has 202,000mi and runs like a champ. As a matter of fact, it runs much like a gas burner. I have been quite impressed with its pep, especially with take off and hiway top end. My problem however, it that on initial start up the idle is so rough that it will sometimes quite. Once it has run a moment or two the fear of it quiting goes away but the rough idle never does, even if driven all day!! I have had injectors replaced, changed all fuel filters, treated fuel, had valves adjusted...I'm at my witts end. Any suggestions??

WD40

When you say rough what do you mean? Is it an oscilation or a miss? If it is a rocking side to side try turning in the rack dampener on the fuel pump.

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82 300SD 100K
91 Caprice SS
92 Jetta TD

Check your motor mounts carefully. If they haven't been replaced in a feww years they could well be bad and the shakes could actually torque the linkage enough to turn you off.