Lexus IS Turbo Wastegate Issue

Sounds like a boost leak to me. That whistling/hissing noise is a classic symptom. Have you checked all the hoses and connections around the turbo? A loose clamp or a cracked hose could definitely cause reduced power and poor engine response, plus trigger the check engine light. Given it's a hybrid, maybe also check if there are any specific hybrid system codes related to boost. I'd start with a visual inspection before throwing any parts at it.

Thanks for the quick reply! I did a quick visual check, but honestly, I'm not super familiar with the turbo setup on this engine. Any tips on where to look specifically for those boost hoses and connections? I'm kind of a newbie when it comes to turbo issues, so any pointers would be awesome. Are there common failure points I should be aware of?

Okay, so tracing the boost hoses can be tricky. Start right after the turbocharger outlet and follow the pipes to the intercooler, then from the intercooler to the intake manifold. Pay special attention to any rubber hoses, as they can crack with age and heat. Also, check the wastegate valve and its actuator arm – a defect there can cause all sorts of boost problems. To be honest, with those symptoms, especially the stalling, it could also be a more serious issue with the turbo itself. At 220k km, wear and tear is definitely a factor. You might want to consider getting it checked out by a mechanic with experience in turbo systems; could save you a lot of headache in the long run.

I took your advice and brought it to a local mechanic. Turns out the wastegate valve was indeed the culprit. The repair, including parts and labor, cost me around 860€. Runs like a charm now, thanks a bunch!