Timing adjustment problem

I have a 96' 240sx and just finished changing my plugs and ignition cables, but when I tried adjusting the timing screw(by the intake manifold) it was extremely tight. When I finally loosened it by unscrewing, neither the timing degree nor the idle RPM change...
Right now my car is running about 5 degrees too rich and I'm burning gas like crazy.
Has anyone been through this before? What do I need to do?

you need to adjust the dist to change your timing. The idling screw is for the idling. Also if you wanted to change your idling you would have to remove the tps first then adjust the restart the car with it pluged back in.