Mustang Engine Whistle Boost Leak

Whoa, sounds like you've got a party of gremlins under the hood! That whistling/hissing IS classic boost leak territory. Have you checked all your hoses and intercooler connections? Any obvious cracks or splits? The actuator fault code could be a red herring, triggered by the system trying to compensate for the loss of pressure. What codes are you pulling?

Thanks for the quick reply! I haven't had a chance to do a thorough hose inspection yet, but I did a quick visual check and didn't spot anything obvious. I need to get the exact codes read again, but if it is the actuator itself and not just a symptom of something else, how would I go about testing that? Is there a way to manually check the actuator's function or resistance, or is it best left to the pros?

Okay, given the symptoms and your description, it really does sound like an actuator or bypass valve malfunction. Trying to diagnose that without the right tools is gonna be a pain. You could try checking the wiring harness for damage but honestly, save yourself the headache and find a reputable shop with experience in turbochargers. A proper smoke test will pinpoint any leaks, and they can use a scan tool to actuate the valve and see if it's responding correctly. It's likely the electrical bypass valve is defective.

Thanks for the advice! I appreciate the insight. Took it to the shop, and you were spot on. Turns out the electrical bypass valve on the turbo actuator was indeed defective. Repair cost me about 250€. Runs like a champ again!