1990 nissan 240sx help!

[ka24depower]

i have a nissan 240sx and i have a header and exhaust on the car.about 2 months ago the car has started idleing weird.the rpms like to jump between 400 and 900 while in park.while its in gear it idles around 500 rpms.when the cars in park and the idle goes up too 900 rpms it makes a whistleing sound.ive replaced the o2censor,plugs,plug wires,cap,rotor button,and injectors.could it be the maf censor or the egr valve.if you can help i would greatly thank you.