Idling on 2008 Toyota Corolla

What do I need to do to improve the idling ? It doesn't idle as smooth as it should.

Asked by for the 2008 Toyota Corolla
It depends on how many miles your engine has on it. It could be due spark plugs, this engine has shim adjusted valves which people forget to check periodically the valve clearance. The throttle body may need to be lightly cleaned with chemtool around the throttle butterfly. You should check that you have no vacuum leaks around the air intake boot or intake manifold. Perhaps have a scantool attached to see if there are any codes or pending codes stored in the computer of your car and if any of the sensor values appear to be out of range.