Well, I have a 300D with the 2.5 turbo diesel engine, and it has roughly 240,000 miles. It has a few issues and I hope to learn more about this car and what's wrong with it.

It's got a really rough idle. When I start it in the morning, it idles fine for 30 seconds or so. After 30 seconds, it starts smoking and shaking. I think it must be misfiring, it produces a heavy white smoke screen out of the exhaust. (I'm going to update this and provide a video clip tomorrow.)(Video: https://my.mixtape.moe/mixdke.mp4). When I start moving, the car is very jerky and it chugs at the lower rpms until it builds boost. After the car warms up, it idles better. (Above 50°C)

After 5 minutes of driving, the turbo stops spooling and building boost entirely. I can tell this from the power output and sound of the car. Very slow acceleration, difficult to reach highway speeds while merging. The vacuum lines under the hood are in pretty bad condition. I've noticed cracks in the rubber, I think they're dry rotted. If someone can provide info on what size I need to replace all of them, I'd appreciate it.

It's also leaking coolant. When I park it on an incline, I notice the coolant level goes down and there's coolant on the concrete. I think I may have found a leak on the return line to the resovior.

Hopefully someone can help me understand what is going on. The car does have paperwork for all the maintenance done, I'm going to take a look at it tomorrow.
Thanks