1992 Other Nissan Models The car idles too high when reachin

I have a Nissan Primera P10 1.6 (GA16DS engine)
It has an annoying problem and so far I cannot find a solution that helps. When I start the car it idles at about 1200-1500 rpm. I guess this is normal when the engine is cold. However when the engine reaches working tempretature it ides at about 2000-2300 rpm. The normal 800 rpm are established almost never. This is very annoying especially when waiting for the trafic lights. Another disadvantage is the increased fuel consumption.