Just bought a 1990 xr2i, engine mods r 4-2-1 manifold full stainless and a k&n pannel filter. The car ticks over about 2k revs and when warm the revs constantly go up n down between 1.5k and 2k revs, also the engine sounds like its whistling. The only time it doesnt whistle is under acceleration. Any help would be much appreciated. Thanks