Sienna Low Power Throttle Valve

Sounds like a plausible cause, given the symptoms. When was the last time you checked the air intake system? A clogged air filter can sometimes mimic those issues. Also, have you noticed any changes in engine idling or a delay in response when you press the gas pedal? A faulty throttle position sensor can also cause similar problems and affect fuel efficiency.

Air filter is new. Engine idles fine. There's a slight delay when I accelerate. You think it's definitely the throttle?

The delay you're describing does point towards the throttle system. While it's difficult to pinpoint the exact cause without proper diagnostics, the symptoms strongly suggest a problem with the accelerator pedal module or the throttle valve itself. Given the potential complexity and the check engine light, I'd recommend getting it checked by a professional workshop. They can properly diagnose the issue and replace any faulty parts.

Thanks. Took it to a shop. Defective throttle valve. Repair cost 265€ including the new throttle valve and diagnostics. Runs great now.