I have an 86 IROC-Z, and lately its been making the wierdest noise(s). I've had three people look at this, and still no diagnosis. My parent's mechanic, my friend who is a mechanic by trade, and I also had it at ELD (they were installing a Dynomax cat - but that wasn't the problem. They didn't do a full diagnostic, but they didn't have any guesses either.)

What happens is the first time I run the car in the morning, it starts out sounding like an exhaust leak in the manifold. After a while it turns to a rattling, but only at idle and on the decel. This problem has been worsening for months - now its unbearable!

However, if I run it for 20 minutes (to work), and let it sit for four hours (before my break), then it runs and sounds fine!

Oh, also - when its making this noise some of my power is gone. A noticable amount too.

Does anyone have ANY ideas? I want to replace the manifold with headers anyway, but I want the problem fixed more. I don't just want to keep throwing parts at it, ya know? Any info/suggestions would be appreciated!

 

Perhaps, a faulty cat with bad internals, clunking around?

 

Carbed?

It's the heat riser valve, in between the right manifold and the Y-pipe.

 

Mark - I thought the same thing and just had the cat replaced. It didn't work :-(

Hopefully it is in the heat riser valve. They are replacing everything from my cat to my engine when my headers get in.

Thanks for the suggestions - I'll take as many as I can get!

 

RB83 - The noise is coming from that area. How difficult is the heat riser valve to replace, and do you know how much $$ I'm looking at?

Thanks again for your help!

 

Man, I got the same thing goin on with my headers. Why does it rattle like that, and how can I fix it? the heater valve that is?

 

I'm not sure. I'm getting some headers early next month, so my mechanic said just to wait, instead of spending an extra $300-$400 now for labor. Blah.

At least then my exhaust system will be complete :-)