My car is high reved at 2000 rpm wont go down

Could be a few things. But here are the obvious. Check for a vacuum leak around the intake. When you put the car into drive it starts putting strain on the engine, a vacuum leak will give it too much oxygen and cause a fuel mixture issue / reading.
If nothing wrong there, you may have a bad throttle position sensor. When you put the car into drive and it starts putting strain on the engine it will pull the idle down then the sensor will adjust it automatically. Hope this helps.

You might have bad connection in wire harness, Wiggle the wires while reving the engine. Do this at night to see any sparks in the dark. Look for sparks around the Spark coil. You may need new coil.

P0068-MAMFQLD PRESSURE/THROTTLE POSITION CORRELATION
' Image
Theory of Operation
This DTC sets when an unexpected high intake manifold air flow condition exists that
can lead to increased engine speed and puts the NGC into a High Air flow Protection
limiting mode. The High Air flow Protection feature includes RPM limits for when a
Throttle and or MAP sensor limp-in fault is present.
When Monitored
During all drive modes.
Set Condition
If vacuum drops below 1.5Hg with engine RPM greater than 2000 RPM and closed
throttle. One Trip Fault. Three good trips to turn off the MIL.
Possible Causes
-VACUUM LEAK
-RESISTANCE IN THE (FS56) 5-VOLT SUPPLY CIRCUIT
-(FS56) 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
-RESISTANCE IN THE (Kl) MAP SIGNAL CIRCUIT
-(Kl) MAP SIGNAL CIRCUIT SHORTED TO GROUND
-RESISTANCE IN THE (FS55) 5-VOLT SUPPLY CIRCUIT
-(FS55) 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
-RESISTANCE IN THE (K22) TP SENSOR NO. 1 SIGNAL CIRCUIT
-(K22) TP SENSOR NO. 1 SIGNAL CIRCUIT SHORTED TO GROUND
-RESISTANCE IN THE (K900) SENSOR GROUND CIRCUIT
-MAP SENSOR
-THROTTLE POSITION SENSOR
-PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.
Auto Repair Help US

First if the "service engine" light is on I would have a local retailer or garage see what the codes are. For possible TPS, IAC, or mass air flow problems. TPS being "throttle position sensor" IAC being "idle air control" If a light is not currently present, listen under the hood for a hissing noise or signs of a vaccum leak.

There r 2 cables on a gt 6 speed that r located at the top of the engine in back.. Do not touch the rear cable unless ur tibrron is shifted hard. The front cable is ur drift idle, theyre 2 nuts tightend den to secure it at a certian level , untighten the nuts and simply ajust the 2 nuts backwards do the cable isnt so tight and allows the engine to drop idle wen accelerater isnt pressed. Then do the same to the rear cable(2nd) cable untill u have ur tibron sounding just right..only sol_tion

check your throttle plate, may be sticking. also check for vacuum leaks around the intake tube and intake manifold.

Clean the throttle body. Check the mass air flow sensor for corrosion of the wire harness connector.

MAF concerns the proper mixture of fuel, not the idle speed, so it is most likely all right (if it wasn't, your car would die before it reached 2000 RPM's). Idle speed is controlled by a small motor, generally mounted around the throttle plate. This is controlled by a computer, which judges idle requirements by the input from crank or camshaft position sensors. Make sure that all of your sensors are clean, and in proper operation.

obdII P1123 is a error refer to Air/fuel controller
OBDII P1123 Fuel Trim Additive, System Too Rich


the obdII P1123 is a error refer to Air/fuel controller


OBDII P1123 Fuel Trim Additive, System Too Rich

the following info is a copy/paste of HMA service:


PRIMARY COMPONENT:

Air/Fuel Control System

SECONDARY SENSOR(S):

Mass Air Flow (MAF) Sensor
Throttle Position (TP) Sensor
Intake Air Temperature (IAT) Sensor
Engine Coolant Temperature (ECT) Sensor
Oxygen Sensors

FAILURE CONDITIONS

If the air/fuel mixture at idle is too rich for more than 30 seconds during two back-to-back trips, this code will be set and the Malfunction Indicator Light (MIL) will be turned on.

Details:


The code will be triggered if the following conditions are met:

Long term fuel trim value (additive) is less than -0.75 ms (-15% to -20%) for 30 seconds or more
Engine speed is less than 880 RPM (1000 RPM, 2.0L Tiburon)
Mass air flow rate is less than 6.1 g/s (7.5 g/s, 2.0L Tiburon)
Engine coolant temperature is greater than 158°F (70°C) [176°F (80°C), Accent]
Engine in closed loop operation
No canister purge occurring

First check for a loose hose or a vacuum leak. If you do not find a leak most likely the throttle position sensor is stuck and causing the truck to idle high. The throttle position sensor sticks, and if this happens you will need to replace it.