Golf IV, High RPM, Error in Fault Memory

Hello, I have a problem with a Golf IV, manufactured in 1999, model year 2000, 1.6 petrol engine, engine code: AKL

The engine is running at too high a speed, approximately 950 to 1100 RPM, but sometimes it also operates in the normal range of 860 RPM. Throttle valve has been cleaned and re-adjusted.
During error reading, the following errors were also detected.

00522 (Coolant temperature sensor)
Signal Faulty:

and 00668 Power Supply B+ (Power Supply Faulty)

The battery was temporarily replaced, but the error persists. After upgrading the generator controller, I discovered that the housing is cracked and exhibits typical overheating symptoms. (Will be replaced tomorrow)

Temperature sensor replaced, but it didn't help.

The errors only appear when the engine starts, but after clearing the error, the errors no longer appear when the engine is running.

PS: The following was also noted regarding the parameters:

The lambda probe does not remain constant, but instead permanently fluctuates between 0.1 and 0.9 volts. As if he's trying to sort things out.

One thing I have to say is that the car already has 240,000 km on the odometer.

Quote:

The temperature sensor has been replaced, but it hasn't made any difference.

Have you checked the resistance value? I think there's a diagram somewhere in this forum showing the characteristic curve. How about the plugs and cables, have you looked into that?

Bye
pax

So, I was able to measure everything again today.

1. Fault found in the power supply cable, specifically near the control unit.

2. Coolant sensor replaced, but the fault still persists. Wiring checked between the control unit and the sensor. The connection is there, so it can't be the cable either. I haven't noticed any defects either at terminals 70 and 53 on the control unit.
Is there currently a make (short circuit) directly on the control unit? Could it be that a solder joint has come loose?

Who can give me another tip?

... maybe the new sensor is also used by the police?
The behavior is consistent with a faulty sensor.

Sensor provides incorrect values, e.g., "Engine cold", resulting in the mixture being "oiled" = RPM increased!

Had a similar error, the cause was the temperature sensor G62.

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Sven