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2012 1.4 L rough idle, bad mpg, missing, when engine is warm

671 Views 3 Replies 2 Participants Last post by  davezolp
Hi All-

I hope someone can give me some direction. I have a 2012 w/ 1.4 L engine and 170 K miles. Engine seems to start and run fine and gas mileage is good when cold. When engine reaches operating temp, things go bad. Rough idle, feels like it is missing, mpg is about 20. I've installed the pcv bypass, replaced valve cover, replaced MAF sensor due to lean codes.

Nothing seems to help. I can't remember where I read it, but I thought I saw that a bad spark plug or coil may cause misfires when it gets warm. Could this be it?

I'm at a loss.
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2015 Cruze 1.4L engine 6 speed AT
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First thing, you need the obd codes read. You can get a good reader for less than $40.

Anyway, ya, the ignition coil could be failing after it gets hot. But it could also be several other items. Like a vacuum leak, you should check all the intake ducts making sure they are all sealed at the joints.
 

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Discussion Starter · #3 ·
I had all the lean codes indicating a leak and decided to do all the replacements (valve cover, cruze kit). Latest code was P0500 indicating down stream O2 sensor that I replaced. (Probably due to the misfire)
 

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Discussion Starter · #4 ·
I had all the lean codes indicating a leak and decided to do all the replacements (valve cover, cruze kit). Latest code was P0500 indicating down stream O2 sensor that I replaced. (Probably due to the misfire)
oops that code is wrong. Can't remember which number it was but it indicated downstream O2 sensor
 
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