Ha HA Ha Ha!!! Talk about out of the frying pan and into the oven with a 2010 Impala! Good luck...
The RPMs jumping around and the rough idle is probably related to the MAF (Mass Air Flow) sensor. Easy to replace and costs around $150. Hope that helps.
I have two 96 Cadillac Fleetwoods, both LT1's, and I removed the Dexcool as soon as I got them. One of them already had mileage on it, and after a year I lost the head gasket. It seems Dexcool is very acidic and eats at the gaskets. If you put Dexcool on an aluminum plate, it will eat on the surface of it. The other Cad with low mileage now has 225,000 miles on it with the green antifreeze with no problems. I do know if you go from Dexcool to green (ethylene glycol), you must use a conditioner to stop the residual Dexcool from causing problems.
I have a 2000 MC SS, and have had the same issues with the key. If you don't let the fuel pressure build up, it will idle rough until it builds up.
Also check your fuel filter; one that is clogged will reduce the pressure in the line. A cheap fix if you ask me. 8 bucks.
I had the same problem with my 2003 Monte Carlo SS. We replaced the hub assembly, and the traction light started coming back on, and now the check engine light. Now the car seems to also have a loss of power and a whining sound, which leads me to believe there may also be a problem with the power steering pump. I am wondering why the loss of power, and why is my traction system still not operating properly? It seems like I have been having nothing but problems with this car. It is a beautiful car; but seems like every time it is fixed, the problems come back, or something else goes wrong. Any suggestions?
I have the same problem with a 2000 MC. Can you tell me what it was, and how much it cost to fix?