What I slow down for freeway speed to City speed blue smoke out and it backfires

What is your question?

Sounders I start it up when I get off the freeway to go to a lower speeds like City speeds 35 40 miles an hour is a backfire sputters blue smoke comes out and then is fine it only happens when I come off from a higher rate of speed to a slower pace pace

What makes this problem better or worse?

Slower speeds

How long has your 2009 Jeep Grand Cherokee had this problem?

4 weeks