Hello All!

Just wondering if anyone has any input regarding my recent install due to a bad o2 and blown cat (o2 was replaced):

Checked the truck this weekend and noticed that one of the o2s was extremely loose. I tightened that one up and made sure the rest were completely tight. I changed the fuel filter as well as cleaned my MAF. After that, I disconnected my battery. My CEL is finally off! I went driving around the past couple of days and noticed some vibrations and other times nothing at all. Drove slow, slammed on it and not once did the CEL come on. Checked under the truck and noticed that sometimes it leaks at idle, but not all the time like before. Also it runs really smooth and then other times you can hear the "puff" at idle as well as feel vibrations. Would a small exhaust leak cause the CEL to light up? As of right now, the CEL is not on. I'm planning on getting more weld done to where the leak is, but was curious if it could be anything else...