I have 2005 MC LS.
When i start my engine,
With Gear is in Park, rpm usually should go about 500 rpm. But mine shifts upto 1000 to 1300.
So i have to turn on and off my car till it return to normal 500 idli g. But it usually happens again while im riding. Wasting gas and harder to brake.
What is wrong with myMC??
And when it shift, it jerks little bit.
Please help. I dont know much about cars.

 

There's a plastic hose that connects to the intake by the throttle body it may be cracked mine did this I have a 01 ss it will make it run bad too it's a vacuum hose