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

check all the rubber breather hoses for splits and that they are secure, it could also be the idle controlle valve require cleaning.

Yeah checked all hoses n pipes but didnt think of the ICV, was reading another thread n if i read it right could it also be MAF sensor??