How long does it sit? oil level and type , correct? Check engine light on? If so , post code #s........ Fresh oil change with a quart of 'Marvel Mystery Oil' added in place of a quart of oil. Clogged converters ,may be causing restriction , not allowing revving over 4K. Check manifold vacuum at idle (from a port on engine side of throttle body).Post reading and if it drops down as the engine warms up.