cold starting problem with peugeot 406 2lt hdi?

This problem seems to be getting progressively worse over the last 3 years and the engine becomes harder to start the lower the temperature, especially when at altitude. If the temperature is below about minus 4 degrees it will turn over and start to fire on some cylinders eventually on all 4 and then to pick up and run without the starter motor assistance. The engine has 170000 miles on the clock and otherwise runs well. It has recently had new air control valve and lp fuel pump.