91 300D Intermittent Major Power Loss

[rholte]

Let me begin by saying that I’ve already searched through past postings, and haven’t found anyone with a problem of this type.

My car is a 1991 MB 300D 350kmi, 5 cylinder turbo charged 602 engine, 50k miles since full rebuild done by Fletcher Jones in Newport Beach, including: a brand new head (all valves and cam), full bottom end, turbo, injectors, and injection pump. The previous owner was a tech there.

The Problem:
It has an intermittent low power problem, that usually occurs when the car is cold, about 30 seconds after beginning to drive it in the morning, but has happened when it is fully warmed up. The car has such low power that it can't accelerate over 20mph on flat ground, and the condition usually lasts for about 30 seconds, and is accompanied by a little black smoke visible from the rear view mirror (about as much as when you really punch it when it is running good). It used to occur only every few weeks, but has lately been happening every other day. I have replaced the fuel filters twice, had it looked at by a few mechanics, and tried different diesel stations but nothing seems to work. The only other problem with the car is a little lifter noise and low power when it is cold, but many have told me that this is normal.
Additionally, while the car is having the problem, there is a slight ticking noise from the engine compartment, and the car seems to vibrate with the accelerator pedal being much harder to push down and almost pulsating. The only possible reason I have heard (from one mechanic) is that the turbo might be seizing against its housing, but wouldn’t this be accompanied by noise, or scarring on the impellor blade and housing (which there isn’t)? In order to stop the problem, I can shut the car down, and then restart it and it will run normally after.
So far, I have replaced the fuel filters, inspected under the valve cover, checked the lifters according to the manual, replaced the glow plugs, checked out the whole intake system for any vacuum leaks or other problems, checked the compression, replaced the air filter, and added synthetic oil. (Some stuff I was just planning on doing anyway.) Also, I looked at the turbo, and noticed a little play in the shaft, but it certainly spins freely, with no evidence of binding.
Where do I go next???