# P0303 Misfire in Cylinder 3. Rough Idle. Not plugs or coils



## joshua382 (9 mo ago)

Replaced all 4 plugs, the coils. and valve cover. then added seafoam to tank to clean fuel system. As it heats up outside for the day it has a real rough time at idle. engine light flashing code p0303. takes a couple seconds to get going but once its going the misfire stops and engine light stops flashing. idling at 600rpm. stabilitrak and traction control lights come on when its misfires too. generally running rough. after adding seafoam and following instructions get home and its not misfiring constantly at idle like earlier but the traction control and stabilitrak lights came on after about a minute and still running rough. its becoming cooler out as it gets darker so i think thats the main reason its not misfiring. when we changed the coil pack and plug it stopped misfiring for a day where before it was a constant misfire at idle. dont know what we changed that affected it.


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## CHEVYCRUZE RS (Mar 29, 2011)

I would take off my intake manifold and see if you could look into each cylinder for any signs of any damage, do you have any current engine codes active?


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## CHEVYCRUZE RS (Mar 29, 2011)

Welcome to CruzeTalk btw


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## joshua382 (9 mo ago)

yeah so the only 2 codes are p0303 and a code for the evap system. its a code that ive replaced the part for once the evap purge valve. but the code stayed on and its been on since i got the vehicle. my parents said theyd also had it fixed. I dont have the code on hand. but yesterday those were the only 2 codes we saw.


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## joshua382 (9 mo ago)

evap code p0449. I went to a shop they recommended a combustion test to insure no leak from head gasket as i feared blown head gasket. they saw too oil had leaked from valve cover into spark plug well so thats why we replaced the valve cover too. replacing coil pack and all plugs like they said and it still persists.


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## Johnny B (Jun 4, 2019)

That cylinder could be running lean. You could replace the fuel injector, or just switch the #3 out with the #1 and see if the misfires follow the injector.

Also, next time you are having a similar issue do yourself a favor. When you pull the spark plugs number them and keep them. I trained eye can tell a lot from seeing a set of plugs.


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## snowwy66 (Nov 5, 2017)

Vacuum leak, bad injector, no compression, no spark.

What's your fuel economy?


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## Kenzya (7 d ago)

_*Hi, u had posted about ur cruze 1.4L.... im having EXACTLY all the same issues thats about to send me to the looney bin! Did u ever find out what was causing all of the issues? Or did u find a magic fix? Im hoping its the magic fix & all I'll need to do is spin around 3 times & then close my eyes & wish it fixed! Somehow I'm doubting those odds tho. 😒 So did u ever get any answers?*_


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## AutumnCruzeRS (Sep 10, 2012)

Check the condition of your battery. Have it tested.


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