So, my car suddenly developed a rough idle and popping(afterburn?) on deceleration. At the exact same time it acquired an exhaust note at idle that sounds identical to a two stroke bike or a chainsaw. There is no loss of power. The noise and the roughness are worst when the car is cold and warming up. It did this a few weeks ago, but only for a day then it changed and the car ran perfect (or near enough) until last Saturday.
Anybody have any ideas or similiar experiences?

 

Exhaust leak?

Lol, if it is, it should be above your avatar and not mine

 

Sounds like a Cat problem to me. I just went through the same thing on my 90.

 

Most likely an exhaust leak - the leak will contribute greatly to afterburn (the popping on deceleration). The reason it sounds worst when cold is, as the exhaust warms up, it expands and the leak fills up a bit.

Dale

 

At first I thought it might be an exhaust leak, couldn't find one. Plus it was there for one day, then it was fine no noise or roughness for several weeks. And when I rev it, even cold, and hold the revs, it sounds just fine.
It's the weekend, so I'll be crawling all over/under it tomorrow.
Thanks for the response.
Still want to hear suggestions, tho.

NOS-Did you replace your cat? If so, what kind?

Suds-Ha! When mine said 'exhaust leak' I thought someone found out about my flatulence problem (not enough!).

 

Well, I found part of the problem. Firstly, no exhaust leak. None, nada. What I do have is a chunk of something in my cat. Either a piece of the matrix or a nut or something (not a stock cat or exhaust). Anyway, I put in a different set of plugs and the car ran better, not great but better. Some build up on the electrodes, probably gas additives. So, I have a bit of misfiring at all rpms and popping in my exhaust on decel. I can smell the unburned fuel. I believe the popping is happening in the exhaust and is bouncing around whatever it is in the cat. The tinny, 2-stroke sound is that thing vibrating and the cat housing resonating. Time to start checking sensors and stuff.