Auto Parts: shocking acceleration, diesel combustion, combustion chamber

Question
Renault Scenic Megane RN1.9D 1998 diesel:
Now and then it loses the acceleration-power as if one tempory takes there foot of the caspedal. So the car is shocking with intervals of a tenth up to a few seconds.
Mostly when the motor is still cold, thought also when warm. Mostly not on the hiway, but this is probably because you don't accelerate mutch.
Thanks for any help, Michel - Belgium.

Answer
    This sort of behavior in a diesel engine is usually a sign of spotty injection performance.  I'm not sure whether the 1998 models employ electronics to control the injection or whether they they use an old-fashioned injection pump.  When the engine is cold, injection timing is much more critical because the cold metal of the engine draws the heat away from the combustion chamber, and this heat is what causes the diesel combustion process to take place.  I would start by going to an auto store and buying a large bottle of Diesel Injector Cleaner (not gasoline injector cleaner, it's entirely different).  Put it in a 1/4 or less full tank and drive for 20 0r 30 minutes on local roads (not the highway) to give it a chance to work.  Then fill the tank with fresh fuel and use the car normally.  If the problem doesn't resolve itself by the time you have used up that tank of fuel, then you are probably going to have to take the car to a dealer and get them to look at the injection.  Bon chance.