How Can I Correct A Weird Idling Problem?

I bought an older 1987 Ranger (clean truck with very low miles) with the 2.3 L engine. Here’s the problem: When you first start it the engine idles and drives smoothly. But when you turn off the engine after awhile (like a trip to the market) and start the engine again it idles really ragged. I checked for vacuum leaks and found none, replaced the EGR valve and oxygen sensor as suggested and still the same thing. It idles fine when the engine is colder but runs ragged when starting it after it’s warmed up. Any suggestions?