I’ve got the same CCC system on my car. It’s not the greatest thing GM ever dreamt up, but it’s given me many trouble free miles. Just to make sure, the SES light is coming on when you turn the key? Does it ever come on while you’re driving or idling? Mine’s super sensitive about rich/lean exhaust, but it couldn’t seem to care less about other things like EGR and CTS functionality. Not like my TBI, which will inform me of any little thing that goes wrong.
When I got mine, the CTS and its pigtail were completely disintegrated so I replaced them. The only way I could tell you for sure if it’s working is with my 34 year old CCC scan tool. Unfortunately, serial data is not as easily accessible on these as on TBIs. It’s worth replacing every once in a while on things that have that type of coolant sensor. And cheap.
Is your mixture control solenoid (MCS) working? It should quickly and audibly go “chicka-chicka-chicka” when you turn the key to ON. This is another thing my Caprice is sensitive about. If the connector at the top of the carb is unplugged, it’ll throw a code immediately. There’s a green test port near the carb for a dwell meter. I had mine professionally rebuilt and setup so I can’t confidently speak to the proper procedure on that and the dwell parameters.
Another thing to consider is the TPS sensor. If the idle voltage is too high, that could be a problem. They more commonly fail with dead spots in them, which would cause bogging, but if the idle voltage is above say 0.6V, that’s a problem.
As you mentioned, the O2 sensor is a worthy consideration.
A plugged PCV line and/or a failed PCV valve can cause issues. If in doubt, replace the valve. It’s supposed to rattle when it works properly. Another overlooked system, is evaporative emissions. There’s a little filter on the bottom of the charcoal canister that I’m willing to bet is crusty, old, and dirty. A bad fuel cap, a clogged charcoal canister, or some issue with the little valve can be problematic. Check your vacuum lines. I had about a million that were broken or completely cracked up.
Finally, I’d suggest you check what the curb idle mixture is set to. It seems to me that later Quadrajets like a more liberal mixture setting, and these are no exception.
This is a comprehensive list. You’ll probably find only one major contributor and a couple of little things that don’t impact your AFR as much but that fixing them will help a little. That’s my experience anyway.
@CorvairGeek might have some other thoughts. Here’s a good page with info on the CCC system to demystify it some. I assumed that you knew how to check most of what I didn’t elaborate on, but if you have further questions, check back, and we can proceed further.
http://www.early3rdgen.com/forum/viewtopic.php?f=11&t=25
