P0123 The first one listed on your screen refers to the Accelerator Pedal Position (APP); The gas pedal. It has five wires at the connector #1 is 5 volt supply, #4 & 5 are the signal wires and #3 & 6 are the grounds and they all run to the PTCM. You can check each. Procedure is in the service manuals. Most people replace the pedal. This code can cause you to lose throttle response.

The lower code P0442refers to the Evaporative Emission System. It will cause hesitation at idle or rough idle when the PTCM activates a test of the system. Not a huge problem, but can be hard to correct.

Fix the APP problem first, clear the P0442 code and hope it doesn't come back. You can drive the car with a small leak in the Evap system and see if it causes any idle problems in the future.

You have scanned the car as a SRT6, but you have a base/limited. You should scan as a SLK 320 not AMG 32; Two different engines and a few other small differences ref scanning.