Having idle trouble

I just bought a 1990 b2200. It ran fine driving it home last night but had a lot of trouble starting this morning. Then when it did it idle very rough. The weather was in the 50's so don't think it's a temp issue. It won't go over 65mph. It is very sluggish and there are trace amounts of oil in the breather. New to these trucks anyone tell me where to start.

From your post, it isn't clear whether your engine is fuel injected of carbureted.. You can do these steps if it is carbureted. Take the fuel filter off and blow backwards through it over a rag. Look for water drops that will collect on the surface of the rag. If you have a manual transmission, the fuel filter is on the firewall on the passenger side. If you have an automatic, I think the filter is located on the frame rail under the bed on the passenger side. If you find any water, replace the filter and put some dry gas in the tank. You can also loosen the drain plug on the tank and drains some fuel into a pan and look for water there. The other thing that comes to mind is the possibility of a bad coil / weak spark. With the engine running at idle, you can pull the coil wire out about a 1/4 inch and look for a strong blue spark. It's about 30,000 volts so be careful because you can get zapped.

So my idling problem was actually because of a fail alternator. I replaced the alternator and minipulated the choke manually and it smoothed the idle out.