DIRTY MAF
Clean your Mass Airflow Sensor with some MAF sensor cleaner or contact cleaner
vacum leaks around intake
Inspect your intake hoses and make sure non are leaking
Inspect also the vacuum caps on the manifold and make sure they are both on
dirty eccentric shaft sensor
Check if your eccentric shaft sensor is excessively dirty and clean it
OLd coils-plugs-wires
Check that they are perfectly clicked in place and in the correct order.
If your coils, wires or spark plugs are older than 4 or 5 years, It's a good Idea to replace them.
More power + better mpg
reset ecu
Sometimes is just an ECU error, and all you need to do is reset it by:
1) turn ignition on, but not the car
2) pump your brake 25 times fast and hard until the oil gauge bounces (it does not bounce on all models)
3) Ignition off, ignition on and start the car
low compression
If non of the above helps, do a compression test and if you have less than 5 BAR consider rebuilding your engine.