My wife has a Peugeot Diesel Van. The last 2 years it has started loosing especially low-end torque, mostly when engine is cold. It is a 2,5 l turbo diesel. Is has 80.000 miles on it. It starts by a flick of the key even in hard frost and iddles fine from first rev. The first minute it will hardly rev up when under load. We have to get a pollution certificate on all commercial vehicles here every other year, and this year they told me it had very low value. Can a Diesel run lean ? What would cause it ?? It doesnt smoke even at full throttle.