Changed plugs on 4.0l as a PM. Since than check engine light on with lean mix code and engine lopes severely at idle when warm. At wits end-Ford garage has changed intake manifold gasket checked hoses, fuel pump and changed wires. Latest diagnosis is bad cam. Engines runs fine under load and no problem until plugs were changed. Any suggestions??

 

Did you check the gap of the plugs and also check to make sure you didn't crush the electrode closed on one of the plugs on installation.