First of all, check for any vacuum leaks in hoses and the air intake duct going to the MAF ...Mass Air Flow ...sensor.....cracked, broken or loose hoses. You should also try cleaning the MAF, Throttle Body throttle plate area and IAC/Idle Air control valve as part of normal maintenance....they can get sooted up with carbon deposits which can affect idle speeds or rough idle and it may not trip a trouble code/Check Engine light. In many cases, the IAC/Idle air Control valve is sooted up with deposits and it affects the idle speed since that device is what the computer uses to control idle speeds....intake air is bypassed around the throttle plate area though passages in the TB which go into the Idle Air Control valve which has a little shutter inside of it which the computer opens and closes or varies opening to control idle speeds.
Remove the device from the Throttle body and clean out the internal passages and shutter area of it with TB cleaner or carb cleaner....sold at parts stores. Remove the air duct to the TB and clean the throttle plate area as well ...soot deposits around that can also affect idle air flow or cause it to stick.
Parts stores also sell special MAF cleaner spray that you can use to clean the sensor but the wire tips are fragile so be careful when cleaning....just spray down any soot deposits and allow to dry.
http://kiaoptimaservice.blogspot.com/201...
Idle Control valve...
http://www.autopartswarehouse.com/search...
http://www.kia-forums.com/kia-magentis-o...
Do an OBD2 code check and pay attention to the trouble codes. Do not buy O2 sensors just because somebody says they "usually" go bad. Yours might last the life of the car and throwing away a good O2 sensor is expensive-crazy. More likely, you have worn out spark plugs. In 12 years, I would be surprised if your battery still holds full voltage. Have that checked.
My friend had a 03 rio that did the same thing his problem was O2 sensor
sensors or needing an injectors cleaning
So my 2002 Kia optima is idling rough. Only in drive at stop lights. If I put it in neutral (or any other gear for that matter) it goes away. I notice the rpms are lower in drive than they are in park. So anytime I accelerate the shaking goes away and it runs fine. The check engine light is not on, and does not throw any codes. I changed the spark plugs already and cleaned the intake manifold. Any one got any clues? I cant seem to be able to diagnose this myself. Thank you for your help.
