First off..I would like to thank all who posted to my original question at the end of October...now the follow-up.

What happened:

The pipe attached to the entrance of the rear muffler rusted off. I took it to a small garage (actually recommended) due to it's proximity to work. I had new pipes/mufflers installed from the Cat Back. (The cat was new as of April).

I went to pick up the car and my check engine light was on. I called the garage and was told that they could not reset it and to disconnect the battery to do so. One of the brickboard members told me to pull fuse # 6 instead (which I did). The check engine light went off and I was happy.

The next day I started the car drove one block and the check engine light came on again....sigh.

I decided to give it a couple of weeks to see what would happen. During the couple of weeks I noticed some distinct changes:

1. The car idles rough now...not the smooth purr like before I changed the muffler.

2. Gas consumption drastically reduced. I need to fill up today after getting only 135 miles for an entire tank....wow.

3. Exhaust smell in cabin when idleling....and worse when backing in reverse.

4. Strong exhaust smell outside of car after driving.

I finally was able to make it to the garage this morning. They opened the hood and pulled the throttle a bit...and said..."it is nothing to do with the exhaust" The engine is skipping.

It is strange how my car was running perfectly prior to the exhaust change. I took it to my usual volvo mechanic (Pro VoVo in Freehold NJ). He is a superb mechanic and gave my car a complete clean bill of health in August.

I thought I would get the muffler changed close to home (Pro VoVo is 1.5 hours from me)....but now I am regreting my decision....

If anyone has any comments suggestions on what could be wrong with my car I would appreciate it.

I was told that the O2 sensor could be to blame...but does a faulty O2 sensor make that much difference?

Thanks again for the previous posts..and Happy Thanksgiving to all.