2003 Hyundai Sonata starts when cold and dies after warming up.

P0340 Ford - Camshaft Position Sensor Circuit Bank 1 Sensor

Read more: http://engine-codes.com/p0340_ford.html#ixzz393ZCFfRt
Site gives possible causes and procedure to replace sensor if needed.

P0340 Hyundai - Camshaft Position Sensor 'A' Circuit Malfunction Bank 1 Or Single Sensor Possible causes
- Faulty Camshaft Position Sensor
- Camshaft Position Sensor harness is open or shorted
- Camshaft Position Sensor circuit poor electrical connection
- Faulty starter motor
- Starting system circuit
- Dead (Weak) battery

Read more: http://engine-codes.com/p0340_hyundai.html#ixzz338zFujgZ

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

It is buried under fuel hoses and vacuum lines follow top radiator hose to engine under fuel line between air cleaner box and head

code p 0320 refers to crank shaft position sensor (CKP)/engine speed (RPM ) sensor---circuit malfunction====causes ---wiring---CKP/RPM sensor ---ECM
code p 0340 refers to camshaft position sensor (CMP) sensor A bank 1---circuit malfunction===causes wiring---CMP sensor ---ECM
following engine work , it is always best to check that all of the harness connections were assemble properly
check for broken wires during the work

P0340-P0345 aeall for the "camshaft" postion sensor. It is going out, or a wire to it is intermittantly shorting against a ground. But, is DEFINATELY in the camshaft postion sensor.

dies in first gear makes noise when clutch is engaged

My online Sonata manual shows these possibilities, but does not identify which applies specifically to 2000 Sonata.
Also, when you talk to the dealership parts counter, you'll need to know whether your 2000 Sonata is (a) 4-cylinder 2.4L MFI DOHC engine, or (b) 6-cylinder 2.5L MFI DOHC engine.
Its easy to tell - just count your spark plug wires.

-- begine excerpt from 2000 Hyundai Sonata Repair guide --

The crankshaft position sensor is located next to the flywheel.
The crankshaft position sensor is located next to the flywheel/torque converter.
The camshaft position sensor is located on the engine near the timing belt cover and under the upper radiator hose.
The crankshaft position sensor is located on the driver-s side of the vehicle, down by the lower radiator hose.
The crankshaft position sensor is located on the engine near the crankshaft pulley.
The crankshaft position sensor is located at the front of the engine near the timing belt.

--- end excerpt from 2000 Hyundai Sonata repai guide ---

I have the same problem, starting today. i was driving and it just died. and when its cold it cranks. but when hot itll start and instantly die.

Most likely yes. It's not that the cam is out of position (that's controlled by the timing belt, so as long as the belt hasn't slipped, the cam is where it should be). What's more likely is that the cam sensor has gone bad, as you're suggesting, and it's not able to tell the computer the position of the cam, or it's telling the computer that the cam is in a position that the computer knows it can't be.

Replace the cam sensor and you'll be fine.