78 240d idle knob.
 

Hey all,

A question regarding cold starting my 240d. I almost always, whether warm,or cool outside, requires the idle knob to be full CCW plus some throttle input to keep it running for about 5secs after starting. Any idea on what may be the cause? Could it be valve or glow plug related? Thanks!

Maybe the cable is out of adjustment? How much faster does it idle with the knob turned CCW? It should race pretty well. Basically you can tell if it is adjusted properly by listening to the idle or watching the linkage as you turn the knob. It should start to increase or move immediately - as soon as the knob starts to turn. If not you may have some slack in the cable which causes the idle to not boost high enough to start without some pedal. You will need a boost at cold start on these engines regardless of the outside temps but the full CCW turn of the knob should provide enough to get it started without having to put the pedal down.

When was your last valve adjustment? Once it starts is it smooth or rough?

Might want to also clean the chamber for the glow plugs. There is a reamer for that. I think your is the old loop style glow plugs. I hear the pencil style is a bit better.
Tom

Thanks for the quick and in depth replies!

The valves haven't been done yet and I have no record of when or if they were done by the PO. I know the cable is working because I can hear the difference in idle when moved. It starts to idle smooth once started, and I am able to turn the knob to full CW at the end of my street and it still stays running. The GP are of the loop style and I will be changing them to the pencil soon. This car will only be my summer car so I am not too worried, but it sill bothers me somewhat, as I've read on this forum that in warm weather I should not have to touch it!

I don't have to touch either of my 240's idle knob in the summer, except to compensate for AC compressor. I think your issues will be solved probably with the newer style glow plugs.
You certainly need to adjust those valves too. Might not solve this, but you won't know until you do it, and if the last adjustment is unknown then you need to square that away anyway.

I recently adjusted my valves-they were very tight, no clearance-and it has improved the idle considerably. My car ran very similar to what you describe prior to the adjustment and now I feel comfortable turning the idle throttle way down. I'd recommend starting there. Alex

This depends on the way your car's idle is set. Many people have their idle set so high, even when the knob is set all the way CW that the car will start when cold without turning it.

If the idle is set a little low, which will be just fine when the engine is hot it will not start without turning the knob. If you don't have a tach then you are just setting idle by ear. I always prefer a hot idle that is on the slower side because it will be easier on the tranny and brakes than one which races a couple of hundred RPMs faster but that setting will allow you to cold start without adjusting the knob...so it is a tradeoff.

Replace your idle cable and adjust your idle..a real easy job.
That was one of my favorite features on the 240..wish the 300 had one.