Gauge Issues

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Hey Everyone, I'm currently having some issues with my 2005 Cobalt. One issue started a couple months ago where i could turn the key slightly (not completely start it) and the fuel needle would go up like normal and then i would start my car and the RPM needle and gas needle would drop below zero, basically as far as it could go and just sit there for a couple seconds and then go back to normal. The car starts no problem. I have not changed anything since it started doing this issue. Also a way to make the needles come up quicker is to rev the engine a bit and then it pops up. Any thoughts would really help.

Also another issue i have been having since i changed my spark plugs a couple months ago is that i will be driving and put my foot on the clutch or take it out of gear and as long as i am moving the rpm will bounce from as low as 400rpm to 1000rpm. It was doing it when it was still warm but its gotten alot worse since it has gotten colder as well. I was driving to work today and I had to slowly approach the gate and show my id tag and the whole time i was slowly rolling to the gate the rpms where going from 400-1000rpm. Also if i am at a stop then the rpm levels will not bounce or move. It will stay constant. I have been told spark plugs would not cause the problems but i have no clue. Please Help. I realllllly want to get these issues fixed!