I got 2 question when you change your belt tensioner ,you also need to replaced the Idler Pulley?

I got 2 question when you change your belt tensioner ,you also need to replaced the Idler Pulley? When I start my car in the morning I feel vibration, then when the engine is getting warm the vibration go away,this also happen when I put in Park for a couple of second, then it go away, Any Suggest what could causing this problem? The car is a 2000 Dodge Durango 5.9 engine only 97, Miles.I got 2 question when you change your belt tensioner ,you also need to replaced the Idler Pulley?if it don,t wobble then you don,t have to change it.I got 2 question when you change your belt tensioner ,you also need to replaced the Idler Pulley?only if there is a wobble in it or it's making a noise. when's the last time the plugs and wires were changed? i've seen this often on a v8 engine slight misfire causes a shake in the engine. if its been a while it's a good idea to change them to be sure. I got 2 question when you change your belt tensioner ,you also need to replaced the Idler Pulley?i agree with ivan, with the belt off move and spin the idler, if it feels dry or growley or has play replace it, also are you referring to the pulley on the tensioner or the stand along pulley, the one on the tensioner will come with one, gates makes a great choice.I got 2 question when you change your belt tensioner ,you also need to replaced the Idler Pulley?Only replace parts that need replacing. With a cold engine remove the belt and shake the idler, any shake or squeal, replace it. Otherwise ignore it, it goes away.