2003 honda elantra engine revs up while in park

idle air control valve any lights on in dash

Check for engine codes related to Camshaft Position Sensor or Crankshaft Position sensor. Replace as necessary.

check vaccum lines. inspect throttle cable and spring. if cable is warren can stop it from releasing all the way

you could have a vacum leak some where in the system that can cause high rpm,also if you have a bad tps(throttle position sensor) it can cause this type of problem.you don`t say if you have check to see what is turning on the check engine light and what code is in the computer.this should have been done and may have help to find the problem in the begining.

On my Honda Pilot I experienced the same problem having difficulty changing the gear shifter from park to drive. I drove it to my Honda dealer and the technician explained that the problem was a brake sensor was worn and needed to be replaced. This is because the brakes must be engaged before shifting from park into drive and that the sensor gets worn over time. As I remember, the sensor and labor to install was somewhere between $25 to $50 to replace. It now works like a charm.

its low on charge

I would check for a vaccum leak if there is not then you might suspect the idle air control or the mass air flow, is there a check engine light on

Transaxel range switch is on top of the transmission forward (radiator side).

throttle position sensor going maybe

I've just had the same thing on my Elantra 2001. I took it to the dealership and they fixed it easily; it was a malfunctioning 'Throttle Position Sensor'. They fixed the faulty connection but they said a new one would have cost about 175GBP (275USD) fitted. Hope this helps.