My 1990 C4 has a few different problems, the one that just bugs me is when the car is just idling the tach is almost at the 3000 mark, then when you get going for example on the freeway the tach is buried?? Why is this?

Same here. Mine is also an 1990 C4. This started about a year ago just out of the blue. I should add, it is very seldom driven. Hasn't been out of the shop in over a year. Was out in it and pulled onto an entrance ramp on I-40 and pushed the throtte down pretty good and the tach red lined. Scared the bejesus out of me. When it dropped down to 70 I noticed the tach was reading 3000 rpm's which is close to 1000 too much. The late 70 early 80's camaros have a relay inline from the HEI distributor to the tach I think it is and this apparently cuts the voltage to keep this from happening. I haven't tried to find if mine has one or not. It was mounted on the firewall just behind the distributor area on the camaros. Too much stuff would have to be pulled off to see if it is there. I would appreciate if you would let me know if you find a solution. Thanks