P0234 Volkswagen - jetta

Question

i have replaced the temp sensor and t stat as i had a t state code/// i then also replaced my engine air filter witch was extremly dirty /// since then i have boost p0234 code coming up and lose power whenever i put the jetta tdi 2003 under load ( up hills mainly ) when i turn off the car and back on all operation becomes normal unitl i go up a hill agian.. please help since i have cleaned the maf sensor and also replaced the spped booster sensor/ still throws code and losses power