My 1984 Mercedes Benz 300 SD has a rough idle specially after start when the engine is at room temperature or around 10 to 20 C (50 to 68 F)
It is so rough that the air filter compartment shakes too much.
After adjusting valves it does not change for better.
With cold engine, if I raise the engine to 1000 RPM it runs with a little vibration and after temperature raise the vibration on engine practically goes away. I was wondering about injection pump timing but in a previuos thread about Timing the feedback was that it is almost impossible IP loose time point by itself.Now the question is:What could be the cause for vibration in idle when motor and transmission mount are good and valves properly adjusted.
Feedback will be appreciated.
Thanks.
Nyck

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Nyck - TX - USA

The injection pump itself basically will not change its engine reference. There may be a slight internal pump change over time but it should be of no consequence.
On the otherhand there is the timing chain that completes the refference loop from crankshaft to injection pump and camshaft. That chain will and does stretch with time. Thats why checking the timing and chain stretch was a factory recommended proceedure every thirty thousand miles I think. So again the injection pump itself does not change it's static refference timing. The amount of chain stretch does it instead. The chain just grows longer with time. That offsets the crank in relationship to the pump and cam.
Choose your medicine if you want to get into this problem. I might first check and deal with the timing for example. If the problem is not there perhaps check the compression next. Followed by having the injectors checked out. Fortunatly before all this I think your model has the rack damper bolt on the injection pump. It can affect the idle. I would read all about it in the archives and check that out first as it is probably the easiest and cheapest possibiliy. Or just contributes to the overall problem.
Even before or right after this step I would also make absolutly sure The engine is getting a good fuel feed with no air entering. Watch your primary fuel filter for bubbles being processed with the fuel as it flows in and out of the small fuel filter. There is always a bubble there so pay no attention to it. Just try to make sure there is not a steady stream of tiny bubbles flowing in and out of the filter with the fuel. Others will post as well and what I mention is only my opinion. It's up to you to balance it with many others.
For sure the injection pump can have it's timing relationship changed over time with the crankshaft. I think you see that now.
Any concept you do not understand just ask questions. There are a lot of people on this site with good knowledge. Certainly far superior to mine. They will and do provide good guidance and help. Soon enough you will also be helping others if you pay attention to them and think. If your problem is only happening with a cold engine you should check your glow plugs out very carefully. One dead or really marginal plug might keep one cylinder off line for awhile. Especially if it had lower compression than it should. Is the car smoking much at rough idle? You might also do a power balance check when the engine is running rough. Loosen one injector line at a time to see if you have a cylinder that makes no difference. If every cylinder line you loosen does make about the same difference it eliminates a non firing cylinder when engine is cool. Also a thought that has little to do with your present problem. It is just my opinion. For people like myself that do not work on cars for a living. Tuning a car is probably not required for a really good mechanic. Their developed sixth sense saves there posterior I thiink. For guys like me it is otherwise.
The sooner you do a total tuneup on a car after you buy it the better for you and the car. The car runs better and when a fault happens you do not have as many things to check. For example you said you adjusted your valves. You know valve clearances are not the problem. If they were done earlier in a general tuneup and excessive milage was not driven since then they would not have been an immediate suspect for your problem. Or if the valves had turned out to be the problem this time it would not have happened at all. Even if a new trouble happened a month from now you already know the valves clearance is probably still good. Same with the timing for example once checked for example. Once your engine is not running right you have to do all these things anyways usually before it is done or they are also a suspect or could remain marginal. You just do not know for sure. It does add confusion and difficulty.
An approach I sometimes use if I really am not certain where the problem is. I just do a good tuneup. Many times I find the problem as I go along. Or a good indicator of where it is. You also get to know your car much better and certain proccedures are so much easier to check the second time if needed. .There was no pressure either when you were doing it originally..So you learnt more. A lot of problems posted on our site would not occur if the cars had a general maintenace schedule followed. I believe it is easier on our heads over the long run. Most important is the better reliability and less money and time required when something goes wrong. It is just so much quicker to locate a problem. Fully 50 percent of the problems I think we experience are a result of improper or no regular maintenance in my opinion. A really high price to pay for neglect. You are tied up. The car is tied up. It costs more money to resolve. The troubleshooting is far more involved and tedious. You experience a far higher percentage of problems as well. Almost everything in the affected area is a possibility. You do not trust the car as much as you have comprimised reliability by your neglect. Lower fuel milage than possible perhaps. Less power than is potentially available as well .Harder time starting especially in cooler conditions. Much harder on your electrical system even if it does start. Leaves you the enjoyable job of changing out the starter for something to do more frequently than required. Glow plug circuit as well. The destruction potential is just increased. You get less owner enjoyment and bonding with your car even though it is just a mechanical item. I have dropped all this into this post as I do not remember seeing it covered before. It is not meant as a fault finding thing. More just as food for thought. It is just common sense really and I am guilty as well on many things I own. That can be verified by my better half. She even informs me occasionally of shortcomings believe it or not.
If any of my four daughters are visiting home they will plunge in on their mothers side as well. I just consider it a gender thing. I really know what a target feels like sometimes. Defensive manouvers are pointless. They are good. But why did they have to turn out as smart as their mother?