stock rpm fluctuating need help...

[240mph]

i am seriously in need of help...ok but my stock rpm needle would just go around like crazy, after my friend tried to hook up the tach coil line to the back of the rpm cluster after i took it out the rpm just goes crazy and when i tighten the screw for the rpm it works fine but then it comes back can anybody help i dont want to spend big bucks just to get a new one.thanks

[thx247]

I'm having serious trouble understanding what exactly happened. Can you reword your question?

[240mph]

my stock rpm on my stock gauge cluster the needle is moving like crazy i tried to tighten the bolt in back of the cluster it worked for awhile but it f***ed up again it started going crazy i hooked a wire from a tach meter to that same bolt in the back of the rpm and the aftermarket tach works like normal but my stock tach is still f****ed up.