Renault Trafic 2002, starting problems?

Hi my trafic has been struggling to start in the cold weather. My local garage has replace the glow plugs and oil filter and cleaned a sensor and it is a bit better now but still not idling properly for 5-10 seconds, then it idles ok. It has been serviced regularly and has about 50,000 miles on the clock. Any suggestions welcomed to save me an even bigger bill! Thanks , Todd