Lets see, a spring hold s the wastegate closed - they have been known to break or the shaft to temporary bind. As far as what opens it, I am at this point unsure. I do at times get the two systems mixed up (the truck and the Mercedes). Manifold pressure does operate the ALDA which increases fuel delivery. Overboost is sensed by the wastegate by I have fogotten what mechanism opens it. The symptoms made think of the wastegate problem, not the method of operation. Having said that, the EGR suggestion is a good one. My truck doesn't have one and both of my mercedes have manage to "grow" a block off plate where it attaches to the intake manifold. 87300SDL-Please post the resolution if your ever find one!

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D. Blake
86 300SDL 340K (for sale)
83 300SD 205K (gone)
06 Chevy K3500 LBZ CCLB 50K
94 Chevy K2500 6.5L TD 250K (gone)