"Lumpy" diesel engine at low throttle

My Peugeot 306 HDi (2 litre, high-pressure direct-injection diesel, manual transmission) has started to become a bit "lumpy" when I apply power or remove it. If I take my foot off the accelerator in order to brake, the car lurches slightly; if I put my foot back on the accelerator after braking, the car surges forward slightly. Not by very much: if I'm very gentle in applying the power, I can accelerate smoothly. But it's gradually become more noticeable over the last few months.

It's as if the supply of fuel is all-or-nothing, rather than being accurately controllable at very low throttle settings. Dirty injectors? I did try adding a diesel injector cleaning additive to a tank of fuel a while ago but it didn't make any difference.

The car is 7 years old, has done about 105,000 miles and has been serviced at the correct intervals of 12,000 miles. At the last service, the cambelt was changed as part of the routine maintenance recommended for the service at that mileage. Fuel consumption is still the same as when the car was new (well, once the engine was run in!) at around 50-55 mpg (UK) or 40-45mpg (US). Apart from the low-throttle "lumpiness" the car still drives perfectly - good acceleration, reasonably smooth running of the engine (as smooth as a diesel ever is!).

Anyone any suggestions as to what the problem could be? I'll get it looked at during the next service, but I want to be prepared in case it's likely to be an expensive repair.

Reply to
Martin Underwood
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