Cold Start Problem

Hi Guys, The wife's car is a 99 Mazda 626 GSI Estate 2 ltr which has a major problem when starting from cold.As soon as it warms up it drives fine but it has no fast idle at all. We had it in to are local mechanic who cleaned out the throttle body and the idle solenoid which seemed to work but only for a few days. We then had it in the Local Mazda agent who changed the throttle gasket which also did the trick for a couple of days but we are now back to square one. It has just passed the MOT with flying colours so all emissions are fine. I suspect that a temp sensor is involved but have no idea where i should be looking. Any ideas or recommendation for a garage in Leicestershire that can sort it out most welcome Morris