I recently bought a 2006 cobalt ss sc. I can't pass emissions because of the mentioned problems. it threw 4 codes: p0304 cylinder 4 misfire, p2101 throttle position performance, p0130 bank 1 o2, bank 1 running rich. I'm convinced these are all caused by each other, a bad o2 or throttle position sensor could definitely throw everything off kilter. The fuel/air mixture is simply horrible, if the number 4 injector is being told to over spray fuel into the cylinder it could easily cause a misfire. But that's just a thought. I replaced the spark plugs, and switched coils 3 and 4 with each other, no change. I already have new coils on the way, mainly because that's just what I do when I buy a new car. I don't think new coils will help, but who knows. I'm gonna be replacing the o2 sensor tomorrow as well. Any help would be very much appreciated.

 

A bad TPS typically won't cause the idle/surge and rich running conditions; they usually throw the car into limp mode and throw correlation error codes.

Does sound like you potentially have a bad O2 sensor though, and that could definitely account for the idle, surging, and rich conditions. You could also just have dirty injectors; there are injector cleaning services all around and they usually have a one day turn around.

OEM coils are quite stout, so replacing them is kind of a waste of time and money - especially if you aren't putting OE-supplier coils back in. If you had a bad one, it'd be more obvious.

 

I installed the new coils and the misfire went away completely. Still a rough idle though, I'm gonna go ahead and replaced the other 2 oxygen sensors and see where that gets me. Also, it seems that the tps code went away as well, not sure why but lets hope it says that way.

 

Ok so I spoke too soon, the car noticeably ran better and had more power, but it threw the misfire code again. It drove great with no check engine for a day and a half, then all of a sudden came back.

 

What spark plugs are in it? To what are they gapped?

I wouldn't worry about the post-cat O2 sensor... it has zero effect on how the engine runs, it simply checks that the CatCon is doing its job.

 

I replaced the ones that were in it, with a set of NGK BKR7E's. Gapped them to .035.

 

Does the car have a smaller S/C pulley? BKR6E is the OE spec, tune + pulley cars run the BKR7E. I wouldn't think that'd cause your issues though. Might have to tighten up the gap later on, depending on blower pulley size, but that shouldn't affect your idle and casual driving.

I'd work on that primary O2 sensor. Potentially a fuel injector problem too.

 

Yeah mine has the 2.8 pulley. I’m getting it tuned professionally on Thursday. Hopefully the defoulers I ordered do the trick for the o2 problem. You're right, it could easily be a dirty injector, I think I'll take the cylinder 4 injector off tomorrow and clean it.

 

Do you know what injectors it has? GM S2 (42#), 60's, 80's? 80's are notorious for getting gummed up very easily. They have terrible idle flow in perfect condition. With that said, most LSJ cars tend to either run 42's or 60's.

Might be easy enough to pull the whole rail, stick each one in a plastic bottle/cup, and give it a crank to see if they're flowing at least somewhat similarly.

 

It has the 60 pound injectors, I'll test out that theory tomorrow. If the 4th injector is indeed gummed up, what would be the best way to go about cleaning it?

 

I'd just search in internet for a place that cleans injectors. I'm sure, at the very least, Atlanta has one.

I used InjectorRX out of Houston for mine. One day turn around - shipped on a Monday, had them back on Wednesday. You could technically use them too, but you'll obviously have more time tied up in shipping.

https://www.injectorrx.com/

 

I switched injectors 3 and 4, no change. I had it tuned today, runs better, still misfires at idle. Next thing to look for I guess would be a vacuum leak.

 

Found a vacuum leak in the cylinder 1 injector port. I used a smoke machine to pressurize the system, smoke was pouring out of the injector port. I'm buying new o rings today.

 

Did you order the ACDelco kit? It includes the cups, as well. That's why I bring it up.

https://www.summitracing.com/parts/ado-217-2257