My car (97 ex) idles incredibly low (maybe 300 on average just below or at the white check between 0 and 1. It has began to vibrate when in idle. I hear a lot of noise on start up and when in idle. Getting 25 mpg when I used to average 29. There is a LOT of movement in the muffler area. I figured it was the cat considering all the problems I am having, but I took it to a shop where they drilled a hole in it and said it wasn't plugged? I probably need hangers too.

The car is burning rich as all the build up under the muffler BUT I know this is a diff issue.. for the most part.

SO my question is.. would a muffler really cause ALL of these problems? Something about back pressure? One shop said baffles or the muffler has NOTHIN to do with back pressure. I'm really confused!

THANKS!