2010 aveo5 LT still runs rough after changing valve cover gasket.

I've found lots of info here for working on my wife's car but now I had to join to ask a question.

She suddenly had a very rough idle and very little power below 2000 rpm. I pulled the plugs and found the middle two were covered in oil. I cleaned the plugs and changed the valve cover gasket. You could see the oil trails where it was running down into the spark plug hole so I'm pretty sure we found the problem.

I just test drove the car for 20 minutes and it's better but the same problems exist. I've got some low end power but not enough and it still idles kind of rough. I pulled the plugs again and they look fine. If there was extra oil in the middle two cylinders I figured it would burn off. Should I try new plugs? Should I try and blow the extra oil out of the cylinders or just drive the car more and see if it smooths out? Any other ideas? Thanks.

I would just change the plugs. Make sure you get the right ones and don't bother with the fancy stuff. After that it might be time to change the wires. The oil gunks them too.

I just changed the plugs, still runs rough. I have coil on plug ignition, not spark plug wires. The middle two had a bit of oil on the ends. I cleaned them with electric cleaner and then blew them dry w/ the air hose. All 4 Coils are connected together. Looks like it's an $80 part. I guess that could be it but I'm skeptical.

It is nearly impossible to clean out all the oil. Replacing the parts is one way, but it will still linger around the base of the plugs.
Is it the exact same? Do you have any codes? Check engine light?

New coil fixed it. I still have a CE light. Code was cylinder 1 misfire but the middle two cylinders have been the oily ones.

I just put in a new coil from autozone, it idles fine. I'm about to test drive it. Idle was rough.

Will my code eventually clear itself or do I need a scan tool. I had AZ pull the codes but I need to buy a scan tool anyway. My friend said he has a plug and a phone app. How well do those work? Can you clear codes with them?

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Originally Posted by shipwreck17

New coil fixed it. ....

Will my code eventually clear itself or do I need a scan tool. I had AZ pull the codes but I need to buy a scan tool anyway. My friend said he has a plug and a phone app. How well do those work? Can you clear codes with them?

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New parts fix everything, YEAH!
I use Torque and my phone with the odbii blutooth. I don't leave home without. Works great and I use the free app.

So a few days later and the car still runs great. I got the OBD2 scanner and phone app. Now we're getting a P0420 code.
catalyst system efficiency below threshold

Should I clean the 02 sensors? Did they get oil on them? Should I just replace one or both of them. Looks like they are $170ish for the pair. That's more than I expected.

Does the front O2 sensor adjust the fuel mapping and the rear just check the cat. Is that correct?

I am still having trouble with that code myself too. I got to the point of just ignoring it. Of course I am a state that does not do a ODBII inspection

We don't have inspection either but the problem started at the same time as the oil leak plus we're not getting the MPG we used to. I'm going to replace the upstream o2 sensor. From what I read trying to clean an o2 sensor isn't worth the time. I found it for $80 on amazon.

Alright anecdotal time, so same premise, different problem with mine, but with the same involved parts! Oil on the spark-plugs and a seeping weepy oily trail down to the exhaust manifold, which has persisted since replacing the valve cover gasket about ~8500 miles ago.

Anyways, if you did it yourself, first off, bravo, I have the 2011 model and getting the actual valve cover off was a pain that i simply could not endure, the little metal brackets that are held together with witchcraft and hatred got the better of me and off to the dealer it went...sorry wallet, but all in all it wasn't that terribly expensive. I usually source my parts from rockauto, which you should definitely be doing, as the prices are basically whole-sale so..keep that in mind. Digression, I found that just letting it burn off the oil that was remnant from the exchange was a grim reminder of why I tend to go overboard on maintainence when i smell that smelly smell..that smells, smelly..Really though, hate the smell of burnt oil.


tangent to the side, the reduced mpg might be from coated o2 sensors, since if oil was seeping into the spark-plug tubes, for lack of a better term, it may have slid down into the cylinder and been burnt in the time between leak and replacement. I would atleast pull them and inspect for visible coating or oily residue.