Q: What causes the RPM's to jump so high on my 2005 Chevy Impala LS with a 3.8 liter engine

If you are having high idle conditions, then you may be having a couple different problems. The first is the idle air control valve may be stuck open allowing too much air past the throttle body. The valve can be tested and diagnosed with a computer scanner. The next thing could be a vacuum leak in the intake manifold gasket or behind the throttle body. A vacuum leak check would find this problem. The last problem may be a throttle body stuck open causing the problem. This can also be tested by scanning the computer and diagnosing the problem through a pinpoint test. Contact a qualified mechanic to come to you and test and diagnose your high engine idle.