I have a 91 Camaro RS and when I first drive the car the speedometer does not work. Then after about 15 minutes it starts working but it jumps up and down for a while and then it finally settles down and works until the car sits for a while and then it doesn't work anymore.

Also sometimes when it first starts working if I let off of the accelerator it will drop back to 0 and when I give it alot of gas it will start working again.

I removed the instrument cluster to see if any of the connection were messed up but there was nothing that I could find. I also checked the VSS to see if there were any loose connections but there were none.

Can someone tell me how to test the VSS to see if it is working correctly and what could be some of the causes of my problem?