i am the proud owner of a 1990 300D (124.128) with over 175,000 miles. i have owned the car for the majority of those miles. i have never, ever had a problem until now. at no matter what engine temperature when ever i press the accelerator to the floor the turbo boost does not kick in until 4,000 rpm. how ever at 1/2 - 3/4 throttle the boost kicks in at the normal 2500 rpm. i have checked all vacuum and pressure lines and they are neither cracked nor clogged. all suggestions welcome.