Van ran very rough during winter until it got cold. Then it ran great. Now that it has warmed up it is back to running rough again. Missing very bad. Last code I pulled up said EGR valve but then it got cold and van ran great so never bothered to change not it is warm back to missing again. Could this be the EGR valve doing this

 

If the EGR valve is not closing completely it could cause difficult starting or rough idle. If it is opening when it should not can cause performance problems.