2001 hyundai accent stalls or just turns off when slowing down.

that autozone sales person should have asked when is the last time it had a tune up... ie, spark plugs etc...

reset the ecu/ecm and clear the codes... see if the same codes come back to verify

look for vacuum leaks first if you already done a tune up by changing those worn spark plugs, etc
P1123 Hyundai Long Term Fuel Trim Error System Rich

P0108 MAP Pressure Circuit High Input

and the 0300's have something to do with your ignition components; i'll let you google those since i googled the first 2 for you

LONG TERM FUEL TRIM FUEL MIXTURE TOO RICH, POSSIBLE CAUSES FAULTY OXYGEN SENSOR, FAULTY FUEL PRESSURE REGULATOR,DIRTY FUEL INJECTORS STICK OPEN,OR ENGINE HAS MECHANICAL FAILURE FAULTY CYLINDER COULD HAVE LEAKING VALVE OR VALVES COULD HAVE INTAKE LEAK.

See if your idle air control valve needs to be cleaned out. This is a common problem in cars that stall out a lot.

During rough idling, when the clutch is released due to high rpm of the engine, the engine may stalls. Another possible reason due to quick release of clutch pedals.

First tune the idling of the engine. Look for the cleaness of the air filter, Fuel lines are clear for free flow. Check the spark plugs for free from carbons and gaps are maintained correctly.

When slowing down the car change to appropriate gears and netural the gears when about to stop.

sounds stupid but the last time something like this happened it was a loose ht lead....but im sure you checked that already.
idle should be 850/900
liquid is only condensate in rear box
have you looked for an air leak in the pipe from the inlet to the brake servo?

Check for a vaccum leak at the intake.

Revs.
As for the issue of the idle revs, that's perfectly normal. When it's cold outside, every car is supposed to have a higher rev in order to warm up the engine quickly. In more advanced cars, the computer wont even allow the engine to shift into overdrive when it's cold outside in order to avoid extreme engine stress and damage. When it's warm outside, the engine doesn't need to idle high because the engine is already at a good operating temperature. Not much will be needed to get it to the right temperature.
Intermittent Jerking

There is a long list of things that could cause intermittent jerking. I'm going to name all of them for you, but your best best would be to go to a mechanic and have them do an inspection.
Clogged PCV Valve (Possibly if you don't get your oil changes on time, sign of a tune up)
Bad DIstributor Cap (not likely at 140,000 miles)
Clogged fuel filter (Very likely, usually done with tune up)
Bad Fuel Pump (Not so likely)
Defective ECM (also not likely)
Vacuum hoses/leak (not likely but possible)
MAS (Mass Airflow Sensor--not likely but possible)
Fuel INjectors (if so, sign of a needed tune up)
Faulty Spark Plug Wires (not likely if tune up is recent)
Faulty O2 Sensors (possibly)

Clogged Catalytic Converter (Possible)
~Hope this helps

I had a similar problem and had an engine tune up done and the car runs almost like new now. Mine is a 2001 Hyundai Accent too.

ive got a 1994 1.3 accent and now its spluttering was does it mean ?

Yes, all these newer cars have them, plus a dozen other sensors.
Try having the throttle position sensor checked, and have a fuel pressure test done.Has it had a tune up lately, plugs wires, and fuel filter changed? Without doing a lot of testing to pin point the problem, you will be replacing things you don't need. (expensive).
A tune up would be a start, then have those other things checked.
good luck.