Last week, I lost my fuel cap, and hadn't given much thought to it until I got the evap emissions code. I replaced the cap then cleared the codes. Since I cleared the codes, my car has been really weird. At first, there was loud random knocks, which I fixed by filling up with gas and adding fuel additives meant do fix the knock. But there is also this weird noise that happens periodically. It is like this deep "wallowing" sound- maybe like running over a rumble strip, but smoother. Along with this sound, the car will feel like it is being held back. This happens for just a few seconds, but often while driving. Please help!!!