Dang you're very knowledgeable! Thanks for all the info!

 

I just thought I'd post a follow-up for anyone who might be interested...

After getting the new catalytic converter put in, and getting that MAP sensor line replaced, and checking all the spark plugs and wires, I could tell that something was still "off". I knew that the EGR valve was bad, so I found a good one at a pick-a-part junkyard and put that in. While I was putting that in, I noticed that the small PCV valve grommet near it was badly cracked and in need of replacement. It's the one that connects to the injector housing, which you can see here. I checked the local Auto Zone and O'Reilly stores, but neither of those had the right PCV valve grommet. I finally checked at the Pep Boys on the other side of town, and they did have the correct one. Getting that working EGR valve, and the new PCV valve grommet installed is what finally did the trick, and my Camaro is now running better than it ever has since I bought it this past February.

Thanks again, 1augapfel, for all your help!

 

Glad to hear of the happy ending. I'm pretty certain that the EGR valve is responsible for the improved performance and not the PCV grommet/elbow. That grommet/elbow is just part of the path that filtered air takes from the inlet duct to the crankcase. If it is damaged or leaking the only drawback (a big one) is that dusty, dirty air will be drawn into the crankcase. No performance affect, short term anyway...

I need to get one of those grommet/elbow pieces too. When I rebuilt my 3.4 I noticed that it was a bit mushy. Good to know I can get it aftermarket.