2001 Volvo XC70 Repair codes P0121 and P1609

(Car is a 5 cyl, but that wasn't offered as an option.)

My 01 XC70 volvo looses power when using heavy acceleration. The message on the display panel reads "performance reduction". We were out of town when this happened and found a local mechanic who could pull the repair codes, but didn't have the computer equipment or the parts to repair it.

The car drives fine so long as we don't gas it while getting on the highway, or engaging the turbo.

The codes are: P0121 and P1609. He did an website search for these codes and deducted that it probably needs a throttle actuator, and guesses we'll pay $1,000 to $1,500 for the repair. Would you agree with this diagnosis?

The turbo was replaced in the past 2 months. I usually trust my mechanic, but lately we're taking it in every 2 months for $500-1500 repairs, and sometimes things need to be redone or related repairs come up. Before I ask my mechanic if this repair is related, I wanted outside advice. Could this be connected with the recent turbo repair?

Thank you