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So I have a 2006 coupe 2.2L 139k with a P0302 code.

I just changed the O2 sensor, spark plugs and oil. (there was a o2 code as well, now it's gone.) The oil and filter looked pretty bad, a little sludgy but not low. The plugs were worn but all in good condition and all looked the same.

The car is not bad except for this P0302 code. What seems strange to me is that it doesn't seem to trigger until the AC is turned on at idle. I haven't driven it enough to verify that though.

It runs great and pulls without issues through the rev range. I don't really get any physical indication of a misfire but I have not driven another Cobalt. It has minor vibration at idle but not very noticeable especially for a 4 cyl. econobox.

I would like to fix the CEL for good. What steps can I take to continue the diagnosis? I checked the spark plug boots and springs, they all seem in good condition. There are no strange noises from the exhaust. No drivebility issues, no overheating or coolant loss. It gets 29mpg.

What can I do?
 

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Which OBDII reader are you using? It should be able to give you misfire counts. This can help tell if you have a real misfire or a freak code. May just need a gas treatment to clear some carbon.
 

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Which OBDII reader are you using? It should be able to give you misfire counts. This can help tell if you have a real misfire or a freak code. May just need a gas treatment to clear some carbon.
Bluetooth and Torque Pro. For some reason the misfire counts don't seem active. I activated the extra PIDs too. I'll try again today.
 

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I tried mine this morning, and couldn't get it to work either. Maybe an update bug.

---------- Post added at 02:48 PM ---------- Previous post was at 02:17 PM ----------

Okay, I found what they did, you now have to tell it which manufacturer you want to monitor.

Start up Torque
Touch the options, bottom left
Settings
Scroll down to Manage extra PIDs/Sensors
Then I selected GM, Pontiac Opel something or other, next to Ford
Then I think it adds the GM PIDs
Then go back to the “Realtime Information” and when you want to see or add the Misfire PID it will be there.

 

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I remember having a code about a month ago dont think it was the exact one but, my father cleared them since i dont have a laptop and it went away and i later found out there was no issue. but if you tried that and it still there then i honestly dont know
 

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Discussion Starter #6
I tried mine this morning, and couldn't get it to work either. Maybe an update bug.

---------- Post added at 02:48 PM ---------- Previous post was at 02:17 PM ----------

Okay, I found what they did, you now have to tell it which manufacturer you want to monitor.

Start up Torque
Touch the options, bottom left
Settings
Scroll down to Manage extra PIDs/Sensors
Then I selected GM, Pontiac Opel something or other, next to Ford
Then I think it adds the GM PIDs
Then go back to the “Realtime Information” and when you want to see or add the Misfire PID it will be there.

Yeah, I tried this. For some reason the PIDs are shown not active. Not sure why. I reinstalled the app but no go....
 

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If you re-installed the APP you will need to re-select GM because it will go back to default which is nothing. Misfires are at the very bottom of the list. They will only be highlighted if you are connected to the ECU.

 

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Discussion Starter #8 (Edited)
If you re-installed the APP you will need to re-select GM because it will go back to default which is nothing. Misfires are at the very bottom of the list. They will only be highlighted if you are connected to the ECU.

I did just that. Still nothing.
Here's something weird though. Today I started it and it was running VERY rough. Sounded like 3 cyl. I shut it off, restart and it purrs.
Even stranger, I reset the CEL, and this time removed the Bluetooth adapter. (I've had it plugged in since I got the car.)
Now, after 3 or 4 starts and a few short trips still no light. Before the P0302 would trigger after even a short run cycle. I think I'll leave it unplugged and just see if comes back.

PS. I also cleaned the throttle body and reseated and cleaned the ICM and ECU connections. Neither were very dirty.

Edit. Check Engine light just turned back on :( Seems to be running just fine though.
 

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Discussion Starter #9
I picked up an ICM from the junkyard for $8 today, figured it was cheap enough to try. No change. P0302 came back after 3rd drive cycle.
I loosened the coil module thing and wiggled it while running to see if it was a bad connection, no change. I think a compression test will come next. Good thing the car was cheap. If it's low I'm not fixing it lol.
 

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Discussion Starter #10
UPDATE:

I thought it would be a good idea to swap injectors. I noticed that cyl. 1 injector was different/ newer. I swapped cyl.2 with cyl1 and what do you know, the code moved to P0301. Looks like I'm getting new injectors! Easy fix! Also seem like this isn't the first time since cyl.1 had been replaced already.
 

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Far out for the injector find.
How old is your coil pack, you might want to find a new replacement.
Even the cheepest new coil from rock auto or ebay or...<$20 to >$50 is better than one that is intermittent.

I blame a bad coil pack on killing a new Cat in less than 200 miles due to P030x.
After much time trying to find the cause of the error,s,
swapped the coil pack and the errors were gone....except for a new cat that was dead
 

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Discussion Starter #12
Far out for the injector find.
How old is your coil pack, you might want to find a new replacement.
Even the cheepest new coil from rock auto or ebay or...<$20 to >$50 is better than one that is intermittent.

I blame a bad coil pack on killing a new Cat in less than 200 miles due to P030x.
After much time trying to find the cause of the error,s,
swapped the coil pack and the errors were gone....except for a new cat that was dead
I'm fairly sure the coil pack has been replaced. It doesn't have the ecotec logo on it. I bet the previous owner was going crazy trying to fix this issue.

I got a junkyard injector for 12 bucks (two actually, just in case) and no codes so far! Super happy!
It seems to run really well!
 

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Glad it is running well for you.
After getting daughter's running right, i found it fun enough to go find one for me.
So then she decides to try hi speed parking. Well that didnt work.....! So she just picked up an 08 LT in SC.
For a test drive, picks up 30 day tag and tries Charlston to KC for it first drive. Oh joy.
Now i find out it has RKE and no key fob and her TPMS system needs training. Well aint that Special
After a minor issue with the vehicle speed sensor poor connection,, she just mad it to KC.
So now the fun begins again. So time for the dumb old thing to learn more tricks. <----<<
And fine the buggs inmher new car. While tring to enjoy my own 08 LS BC.

But I do enjoy bopping about in it. Much more fun the an F-150-7700 or Town Car. Nothing like a Land Yacht.
BTW i bet a 5 sp would make a decent Toad
 
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