Misfire during warm up
 

I have a 1994 Ford Econoline 150. It starts fine hot or cold. The issue I have is that after starting it cold, it runs okay at first, but after about a minute, it begins to misfire a bit. It continues this until the engine reaches operating temperature...then it runs okay (though it seems down a bit on power). New plugs, wires and cap/rotor did not solve the issue. All the old plugs looked okay. It has a V8 engine, but I'm not sure if it's the 5.0 or 5.8. Intake says 5.0, emissions sticker and VIN indicate it's the 5.8...go figure. It's the original engine, too.

Any advice is greatly appreciated.

Should add a couple more details:

It hasn't been driven much over the years, has only 34,700 miles on it.

The misfire used to be worse, but lessened after I tied up part of the exhaust system that came apart...maybe a coincidence, but I thought some exhaust back pressure might have played a part in the issue. (Don't let the low mileage fool you-this thing has led a hard life and is a total beater).

37K worked hard, It could be anything from a cracked vacuum line to bad injector signals, partially clogged cats, did you pull the codes?