1990 Renault Clio juddering and wanting to cut out

Sitting in car and left it idling while waiting for someone. It is cold and snowing. Headlights on and kept the snow button going that's supposedley for extra traction in this weather. A while later put it into drive (it's an automatic) and its starts juddering and wants to cut out, which it eventually did. Started with shudders and struggle to put into drive and had to keep the revs up using accelerator. Started driving and still wants to cut out but after a while it settled down again. Temp guage only at midway slight smell of heat. Worried now that this will happen when stuck in traffic. Could it be the snow button being over used, overheating through extensive idling, lack of coolant? Any ideas?