2002 Elantra revs too high

2L GLS 168112KM Revs at 3k in neutral and will oscillate between 3K and 1K some times when in neutral. The car is reving high in all gears also. I have changed and gapped all of the spark plugs
The codes that keep coming up P0303, P0133, P0121, P0441, P0507
I have been the only driver and she has been great up to now.

Your codes are the following:
P0303 – Cylinder 3 misfire
P0133 – O2 sensor (before converter) – slow response
P0121 – Throttle positioning sensor (TPS) problem
P0441 – Evaporative emission control system – purge valve stuck open
P0507 – Idle control system – rpm higher than expected

The P0303 could indicate spark plug wires if the plugs are good. Go only with the highest quality wires as this engine is sensitive to poor wire issues
P0133 indicates that your O2 sensor may be bad and need replacing (part is usually expensive)
P0212 indicates the TPS may need replacing, around 50 bucks
P0441 is a dealer only serviceable item, and job will run about 125 – 150 bucks.
P0507 looks like your problem with the idle, which is possibly related to the idle speed control actuator. It may be stuck due to buildup, and may only need a good cleaning with carb cleaner, otherwise its an expensive replacement.
I suggest getting a Haynes repair manual if you don’t already own one for more help on addressing each of the points above. Good luck!

Are there any situations common to a #3 misfire and TPS a code that should lead me to a solution on an '02 Elantra?