That is fairly normal for an old car that has spent its life doing short runs (or doing nothing). What I'd do is change the oil, oil filter and air cleaner. Then fill it up with Shell V-Power Nitro+ and take it for a 100 mile run. You should get 30 - 35mpg on this run, and, once The V-Power gets to work, it should help to clean up the car's fuel system. Or you could put it in for an engine fuel system Terraclean (www.terraclean.co.uk). Alternatively, if this is the facelift Primera P11, it has a ‘Hypertronic’ CVT with electronic manual hold on six ratios, and this might be where the problem lies.