08 Cobalt Tach problems

It’s not a large problem, but it’s something that could be here for a small discussion. I’ve got an 08 Cobalt LT with a 2.2L Ecotec and the tachometer but it’s off by 200 or so RPM (I plugged in the OBDII scanner I’ve got), but when I have the car in neutral and I hold the throttle so the engine runs at about 2 grand and let the engine go back to idle, but the tachometer hangs around 1500 RPM before dropping back down. I have a video of it saved and can upload it/share it if it becomes hot for discussion. Is there any theory as to why this and if there’s any possibility of a remedy for it? Again, it’s not a huge problem being I drive a clutch and know when to shift, I just want to spark a discussion.