2002 hyundai accent wont rev passed 2500 rpm,

Try changing your fuel filter, if that does not fix your issue I would have the catalytic converter changed.

check IAC idle air control valve. clean with spray carb cleaner.

sounds like your Idle air control Valve

check for dirty fuel filter at engine,,,also you can try one more additive...SEAFOAM...nine bucks a can...add to your gas tank, the trhottle body...follow direstion on the can....don't be alarmed that the engine might smoke...it is temporary and usually fixes fuel problems caused by dirt of carcon build ups....houpe you can use this info

Check the idle air control valve for carbon buildup. Also check for a vacuum leak.

http://ricksfreeautorepairadvice.com/bad-idle-air-control-valve/
High idle rough idle Ricks Free Auto Repair Advice

Sounds like a coolant sensor problem. It signals the ECU for open loop, cold start rich, high idle, until warm up is reached.

P0734 = 4th gear incorrect ratio (that's the torque converter 'lock-up' clutch - inside the converter).
P1401 = doesn't exist for 2002 Hyundai Accent's
P1401 exists for 2000 Accent = DM-TL Air Pump Motor Curent Draw is higher or lower than expected (normal is 17-36 mA). DM-TL = Diagnostic Module for Tank Leakage & is part of the Evaporative Emissions Control System.

These two DTC's are not associated/part of the Accent's Engine Managemenet System (EMS).
Best to have a qualified/certified Hyundai Service Technician properly diagnose this starting problem with your vehicle.

I would check for any vacuum leaks. Also check the idle air control valve. Spray some Gumout around the vacuum hoses, if you get any change in idle, check for cracked or broken hoses. Check Engine Light on?

Have the turbo checked out.

Look for a vacuum leak somewhere. This is the most common problem for a high idle.