Skoda Superb Engine Issues

Reduced engine power and a whistling noise definitely points towards a turbo issue. The check engine light is also a telltale sign. First, have you checked for any obvious leaks in the intake pipes or around the intercooler? A split hose can cause similar symptoms. Also, what error code is the check engine light throwing? Knowing the code will help pinpoint the problem. It could be a faulty pressure sensor, or perhaps a problem with the turbo actuator itself. You mention poor engine response, is it consistently poor, or does it come and go?

Thanks for the quick response. I haven't checked for leaks myself, and I don't have the equipment to read the error code. Is there a way to diagnose a faulty turbo actuator without special tools? Also, is the electrical bypass valve related to the boost pressure?

The symptoms you describe are consistent with a faulty electrical bypass valve, which directly affects the boost pressure. The valve regulates the pressure generated by the turbocharger. A defective valve can indeed cause those symptoms, including the stalling and higher fuel consumption. You won't be able to easily diagnose this at home without the right diagnostic equipment, particularly to check the turbocharger's performance. It's best to take it to a workshop. The pressure sensor might also be faulty, but from what you are saying, a defective bypass valve is a very likely cause.

The garage confirmed it was indeed a defective electrical bypass valve, exactly as you suspected. Replacement cost me 250€. Thanks for your help!