i have a astra 1.7 turbo diesel and when it is freezing outside it struggles and takes a very long time for it to start but when yemperature above freezing starts ok
check for voltage to glow plugs with ignition on and cold engine, if ok and over 80,000 miles replace glow plugs. or possible tight tappet clearences, should be 6 thou inlet and 10 thou exhaust,try that and good luck.
