[SSDan]

Originally Posted by Wontspeak

Mine.

You can take it to the dealership and hope they are competent and fix your car like they did for Wontspeak.

Originally Posted by bdavies11

Most likely a grounding issue. Myself and many others had the bouncing tach on hot days, along with the hot start issue. I followed SSDan's guidance a couple years ago at this link https://www.camaro6.com/forums/showthread.php?t=586153 and it fixed both my issues at once. Haven't had a bouncy tach since.

No reason not to give it a shot. It’s quick, easy, cheap and even if it doesn't help the tach, it won't hurt anything.

Or you can follow the link provided and add your own ground cable. Either way a solid engine to body ground will likely fix your problem. I took the easy route and added my own ground cable.