Checking and cleaning the turbo actuator linkage sounded like a good next step in my troubleshooting.... the P0234 code. ... I was able to clean and lubricate the turbo actuator linkage ... This cleared the P0234 code and restored normal turbo operation.
Trying to get in a quick ski trip last month, I did an oil/filters change, grabbed the dogs and only made it about half an hour out before going into Limp Home Mode (LHM). When I saw that the Intake Air Temperature Sensor (and everything around it) was covered in oil, I figured it had to be a split hose, so I replaced the sensor and the intercooler hose. But the old hose showed no signs of a leak and the LHM problem remained, producing a check engine light and P0234 code.
This morning, resolving to solve the problem, I spent most of the day trying to catalog all the possible causes of Limp Home Mode with a P0234 error code. Checking the easy things first, I grabbed a neighbor and had him press on the accelerator while I watched the turbo actuator linkage. Nothing.
Then I removed the heat shield and found that the actuator arm moved freely, and no wonder because the linkage was dangling below it. Assuming that it's supposed to be connected to something, I'm praying that's my entire problem.
Next stop, figure out where and how to reconnect that arm. Maybe we'll be able to get away for the Fourth of July after all. The fireworks around here make the dogs miserable.