Hey guys! I bought this 2006 Cobalt SS/SC about a month ago. I got it for a pretty fair price as it needed some general things. One thing that needed to be done was exhaust. The car had a complete exhaust, headers back. Some idiot decided that since the gasket was leaking where the exhaust bolted up to the header to weld the flange all the way around (or at least as much as they could reach), and also welded the flanges where the cat back so to speak would bolt up. The cat acted like it had been gutted, or just blown out because I was getting a CEL sometimes about the cat. I don't remember the code, but it was saying the cat was bad.
Anyway, I bought an eBay header and down pipe (catless), long tubes so to speak and got them installed 2 nights ago. My secondary o2 sensor wires were not long enough to reach (it had already been a long night and I didn't feel like extending them), so I had left the plugin where the secondary o2 sensor would go and drove it to work the next day. The car has always had a high idle issue since I got it, and figured part of it was due to the exhaust leaks before the upstream o2 sensor. Anyway, so it still had a high idle after I got the exhaust work done. No big deal, figured has to be something else right?
So last night I extended the wires for my downstream o2 sensor and plugged it in. I drive to work this morning and I notice that when I had my cruise control on, that it seemed to let off the gas a little and pick back up. At first I thought that it was the cruise messing up as I rarely use cruise anyway. So I kicked it off, and even with my foot on the gas it was doing it slightly at times. I glanced up and looked at my wideband, and it would go lean (like you would let off the gas causing a spike lean condition). The idle on the other hand was pretty tame, as it was better than it ever has been (which I thought was weird, because the secondary o2 should only tell the ECM if that cat is good or not right?). EXCEPT, when I came to a stop, after about 15-20 seconds, the car would start chopping at an idle. I could fix it momentarily by reving it up, then another 15-20 seconds it would do it again. I also noticed that when coming to a stop, it would "hunt" for an idle, but then it was fine.
Perhaps hooking up the o2 sensor last night was all a quinkiedink and completely unrelated...Any thoughts? I have 3 different scan tools, Snap-On Modis, Autel MS-906, and a Launch x431. I have not hooked any of them up yet, but they don't always tell you what's wrong either lol.