Hi, I am having a problem with my 1994 nissan primera. It is a 1.6i 16v manual, abs and pas.

It has started having an unusual problem, when I stop the car at say, traffic lights, the revs of the car is still high, as though the choke was still on but after about 4 or 5 seconds, the revs slowly return to idle. If I rev the accelerator pedal, the same happens. I have looked around the carb to see if there is anything that might be stuck, like the cable or linkages, but cannot find anything at all; I any case, it seems too consistent and deliberate a problem to be something sticking. I have also noted a rise in fuel consumption of about 8% on a full tank.
Has anyone any idea what the problem. I don't trust most garages these days so before I think about going to one, I would like to try and fix it myself or be armed with the info as to what it is before going to the mechanic.
Please can anyone help.
Thanks.
Soundssupreme