I have a 240D manual that was converted to a 5cyl non turbo. The car starts and idles smooth for about 5 seconds, then starts to stumble just enough to make the car shake really bad. If I rev it up a little, it runs smooth. The GPs are new, and it has a new set of rebuilt injectors. The valves have been adjusted. Once it warms up a little, it is okay.

Any ideas? Thanks.

rtykw2,

Sounds like the idle speed adjustment is not set correctly. If the idle speed drops too low the engine mounting system natural frequency may coincide with the reduced engine vibrating frequencies. This causes the engine mounting system to amplify rather than attenuate these vibrations. Or, the mounts themselves may be aging, which stiffens them and raises their natural frequency and leads to the same issue.

240D's have a manual idle speed adjustment knob on the dash next to the steering wheel (left of it). I think non-turbo charged 300Ds had the same things. If you did not hook it up when you made the transition, it is feasible this idle speed adjustment is at the heart of the problem you are experiencing. When it is cold out my 240D idle speed goes from a low that can barely support the engine idling to, when fully advanced and I get a reasonable idle when cold, it responds with a very high idle when warm. You have to be careful not to adjust the idle speed too high when cold or it will run away when the engine warms up, which is not a good thing.

Good luck and I hope this helps. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)