Engine light came on and I took it to advanced auto, they did one and told me it was the cat. converter. then i took it the mechanic, he did his own and agreed. but he put it on wrong. everytime i go over a bump there is a loud knocking in the back end. they are fixing it for free obviously but i want to go somewhere else about the exhaust (or whatever the problem is) and have an idea of what its going to cost to fix.

 

Well if they did the diagnostics an if the ignition/ pistons aren't to blame for idle. Then I would start looking at vacuum leaks. So I guess you're headed in the right direction.

 

That sucks that you're getting the run around, and questionable service..