I just bought a 2003 F350 and when I start the truck it runs fun for a while but then the idle starts jumping up and down. it blows black smoke when I start out but does not do that at higher rpm although the it still will push the rpm's up and down. Have never owned a diesel before so not sure whats happening.
any help would be appreciated.

 

So one common issue for this engine is a sensor starts to fail, and the main symptom is surging at idle. The solution could be as simple as just replacing the sensor and wiring pigtail, which will run you $150 for parts and a couple hours of your time. The bad news is that on your particular year getting to the sensor to do a couple of tests is a minor PITA because it's buried on the rear top of the engine behind the turbo, but an hour of your time could save a couple hundred bucks at a dealer.

To confirm my guess-diagnostic, the best deal going is to buy a $20-30 OBDII bluetooth adaptor from somewhere like Amazon, and buy the Torque Pro app for about $5. More info for that is listed out in this thread, plus more options if you have an Apple phone, or want a dedicated device to leave in the truck. The $40 it takes to get Torque Pro running is honestly the best investment you can make for your truck, the data it gives will save you a lot of time any money being able to do some basic diagnostics yourself.
https://www.ford-trucks.com/forums/1...eral-info.html

For my guesstimate, one test is to unplug the ICP (injector control pressure) sensor and see if the issue goes away. I can't see web banners at work so I can't put up pictures like I normally would to show you where all this is, but this thread should show similar pictures:
https://www.ford-trucks.com/forums/1...cp-sensor.html

The sensor that he's replacing is the one you need to unplug, then start the engine with it unplugged to see if the issue goes away. That's a free test to do while waiting on the adapter to come in so you can check some data points to make a better diagnosis.