I had installed a set of used Edelbrock TES headers, and I had ran them open for a few weeks while I was saving up for a custom dual exhaust set up.

My car idle'd EXTREMELY lopey, I could hear that cam just chuggin' away. My car ran like a raped ape! It was so lopey you would of sworn I had something bigger than a 305

Since then, my stock manifolds have been reinstalled, my car no longer has that incredibly lopey idle, and I'm starting to be leary that maybe my cat is plugged, or atleast being a huge restriction. And there *seems* to be a slight dip in performance compared to the open headers (duh) but I just have this feeling that my cat is plugged.

As to why I'm running manifolds again...don't ask, you don't want to know.

 

How much of the TES did you have installed: Just the shorty headers, or headers & y-pipe?

From what you've said, I'd guess just the headers, which were open at the collector. Unlike long tubes, shorties don't make for a good open exhaust from a pulse tuning viewpoint. So, it's not surprising that they would chop up the idle a little bit.

What you're probably experiencing with the factory manifolds back on is "factory manifold restriction", not plugged cat. It is also very likely that some of the improved performance was "loud exhaust percieved performance increase syndrom", also know as "LEPPIS" - a wide-spread but relatively undocumented malady (very common in some circles; no inference intended).