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My 2007 LS coupe is starting to misfire on cylinder #1. Its got about 104,000 miles on it and will at random times start to idle a little rough, the transmission starts to shift a little harder and the check engine light comes on. The code it always throws is P0301. Part of the problem is it isn't consistent. It will be fine, then do it again then stop again etc..... I did the 100,000 mile service at around 95,000 miles (replaced the belt, spark plugs, trans filter/fluid, and oil/filter) It wasn't to long after that that it started happening. I switched the #1 spark plug with cylinder #2s and I swapped the coil wire/pack from #1 with #3 to see if the misfire would switch to those cylinders but the OBD code stayed as P0301. So i did a compression check and wound up with:
#1 - 120#s
#2 - 210#s
#3 - 180#s
#4 - 180#s

So I'm starting to believe my piston rings or head valves are leaking by in cylinder #1. but before I start tearing apart the engine, is there anything else I should check? I did notice the bottom thread of spark plug #1 had a little bit of wet oil on it, would this lean more towards the valve seals in the head leaking by? Also thing I noticed that seemed odd was when I have the oil fill cap off with the engine running, it blows air out of the hole, shouldn't it be sucking a vacuum? When I check the oil, the level doesn't seem to be dropping and the exhaust doesn't really show signs of burning oil. Any ideas?

Thanks

Paul
 

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You must be using an ethanol blend. Try using GM's engine treatment or seafoam to clear some of the carbon build-up.
 

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I think it's up to 10% they don't have to post it at the pump. 15% they have to. The Cobalt engine isn't designed for ethanol. Long term use does what you are experiencing. Don't wait to long or you might do worse damage. Seafoam will soften the carbon clumps and dislodge them from rings and around valves. If you re-do a compression check after the seafoam treatment and it has improved keep putting it in until you are satisfied with the cleansing. Try and find ethanol free gas also to stop the snowball effect.
 
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