New to board, 1.8t question

[sloinker]

Howdy, nice to find a board that has such a wealth of info.

A few months back my emissions workshop light came on and my wife brought the car to the dealer, two valves and some vacuum hose were replaced along with the rear brake pads and timing belt tensioner. The MIL light was reset and everything seemed fine, fast forward 3 months and I have moved halfway across the country from Seattle at sea level to Casper at 5300 feet altitude. After being here a month the mil and emissions workshop indicators came on. My wife again took the car to the local dealer and he replaced the fuel filter. The mil stayed out for one day and came back on, he can't fit me back in for a month and I am kinda leery of using the local VW dealer as I think the service department may be inadequate. In the meantime I have purchased an OBDII scanner which delivers a code 171, left bank lean. I have looked everything over and haven't discovered anything physically amiss or any broken vacuum lines etc. The only thing that does puzzle me is the waste gate actuator, I can reach the slug from the vacuum amplifier and physically move the wastegate about 3/4 inch away from the actuator but when I apply 20 inches of vacuum to the vacuum amplifier nothing happens. Is the amplifier supposed to push the waste gate open, am I right in assuming that a vacuum signal is used to actuate the waste gate? Any help or insight would be welcome. By the way all the coil packs were replaced under recall about 20k miles ago and the car currently has 57k miles.When the mil light comes on the car seems to lose some power and MPG, not a lot but some, also the turbo doesn't seem to spool up like usual when the light is on. I have experimented and cleared the code fault a few times and driven it and then after a couple of trips the fault is back.

Thanks again

Wes