[Joel5.0]

Check the vacuum lines, you might have left one disconnected or, disconnected one by mistake when you changed the air filter and it's affecting the idle control. LUK

 

[Joel5.0]

Check your emissions decal under the hood, the vacuum diagram is there. Just go over the air filter area and check for any disconnected lines, you could also check with the engine @idle for any hissing sound indicative of a disconnected/broken vacuum line. GL