2004 Kia Optima P0303 code

Check/clean or replace the CKP

CRANKSHAFT POSITION (CKP) SENSOR
The Crankshaft Position Sensor is a Hall-effect sensor that senses the Crank angle (piston position) of each cylinder and converts it into a pulse signal. Based on the input signal, the ECU computes the engine speed and controls the fuel injection timing and ignition timing.
Fig. 107: Locating Crankshaft Position (CKP) Sensor

I only have one CRANKshaft position sensor listed for the 4 cylinder model ... (you may be getting mixed up with the CAMshaft position sensor) .. the CRANKshaft sensor is located behind the timing belt covers just above the crankshaft/timing belt pulley and has a long wiring harness going up to the top of the engine .. this can be a very tricky part to replace as you have to thread the wiring loom .. the book time (labor) for this repair/replacement is 2.7 hours !

Hope this helps

Did you clean the signal wheel on crankshaft pulley?

THROTTLE BODY CLEANING
TECHNICAL SERVICE BULLETIN
Reference Number(s): FUEL 010, Date of Issue: September 01, 2005
KIA:All
VOLUME:3
GROUP:Fuel

Related Ref Number(s): FUEL 010
ARTICLE BEGINNING
SUBJECT
This bulletin provides information relating to throttle body and plate cleaning on all Kia models. Residue from fuel additives and/or carbon deposits that result from normal fuel combustion can accumulate on the throttle body and/or upper combustion chamber over time. Dirty throttle bodies can cause a variety of vehicle drivability concerns and may result in MIL illumination under certain circumstances.
When the engine is started, the incoming air sometimes carries residue back to the throttle body and deposits it just behind the throttle plate because of the sudden drop in air pressure behind the plate.
When the engine is running, crankcase vapors enter through the PCV system and work their way into the intake system. These vapors carry with them residue which accumulates on the idle passages and throttle plate. This build-up eventually blocks the air gap between the throttle plate and throttle body bore, causing less airflow while the throttle plate is closed. Over time, the computer compensates for the reduced airflow with fuel trim adaptive logic adjustments, as it becomes more difficult for the computer to control the idle, especially when coming to a stop or when the throttle is "snapped". Do NOT replace the throttle body before the throttle plates are cleaned for any condition related to fuel trim values.
Fig. 1: Identifying Throttle Plate Cleaner
THROTTLE BODY CLEANING PROCEDURE
Remove the intake duct hose that is connected to the throttle body.
WARNING:Make sure the application straw is securely attached to the throttle plate cleaner nozzle. Failure to do so may result in a straw that has come off and is now stuck in the intake manifold assembly.

Fig. 2: Throttle Body
Using throttle plate or equivalent cleaner, open the throttle to the Wide-Open-Throttle (WOT) position. Clean out the throttle body bore and throttle plate using a small soft metallic (brass) or stiff bristled brush as necessary.
Fig. 3: Cleaning Throttle Body Bore
After the cleaning is complete, reinstall air intake duct hose. Be sure all throttle cables are routed correctly then, start the engine. The engine will run rough until all the throttle plate cleaner is burned off from the internal vacuum circuits. Shut engine off.
Remove the ECM memory fuse for 10 seconds and then re-install. This will reset the fuel trim adaptive values. Not all models use the scan tool to clear the adaptive fuel trim values.
NOTE:Removing the ECU memory fuse will not affect the loss of voltage to other control modules requiring the windows to be initialized, ETS, sunroof, overhead displays, radio station presets.

ECM Memory fuses are as follows:
ECM MEMORY FUSES
Model/MYECM Memory Fuses
2001 2005 Rio10 Amp Underhood ECU Fuse
1998 2004 Sephia/Spectra (1.8L Engine)10 Amp Underhood ECU 2 Fuse
2004 2005 Spectra (2.0L Engine)30 Amp Underhood ECU 2 Fuse
2001 05 Optima10 Amp Underhood ECU Fuse
2004 05 Amanti10 Amp Underhood ECU Fuse
2002 05 Sedona10 Amp Underhood Powertrain Fuse
2003 05 Sorento10 Amp Underhood Powertrain Fuse
2005 Sportage30 Amp Underhood ECM Fuse

Road test the vehicle approximately 2-3 miles before returning the vehicle to the customer.

Hey.

Arrowed is the timing belt side of engine !

A bad 02 sensor should not cause one cylinder to misfire .. could you please check for any vacuum leaks on vacuum lines and check the PCV is functioning correctly ... also check compression on all cylinders !