Do you have any trouble codes?
Try this trick to read them:
Extracting Fault Codes:
Without ever starting the engine Turn the ignition switch ON, OFF, ON, OFF, ON and observe the CHECK ENGINE LIGHT. The CHECK ENGINE LIGHT should begin to flash a series of codes. The flashes will be separated by short and long pauses. The long pauses separate the "ones" and "tens" positions, and each code from the next. A code 55 will be displayed at the end of the test.
Also, look through the throttle plates and see if you have any oil pooled up. If you do, then the plenum pan gasket is leaking. Fixing this would fix an oil consumption issue and fix power loss. (you can get an aftermarket aluminum pan
with new bolts and gasket and the fix will last a lot longer, but costs more.)
Lastly, I would check the IAC valve in the throttle body. It can get pretty dirty and nasty, pull it out and clean it with throttle body cleaner. DO NOT put any force on the plunger, you may break it. Reset the computer after doing this so it can relearn where to keep the plunger for proper idle.
The only other thing I can think of after all of that would be a bad O2 sensor, or a clogged catalytic converter.