Poor Running Cobalt...Questions?

Joined
Jun 1, 2004
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Va
My 2005 Chevrolet Cobalt 2.2 with a 5 speed and about 108,000 has just began to act up and finally tripped a check engine light. Details are that the car runs great until it warms up. Then the engine begins to get a random miss from idle through part throttle. Anything more then half throttle and it runs great. I took it to a friend's place and hooked it to a engine scanner. It indicated a P0300 random miss fire and a P0106 which is Map Sensor out of range. The scanner also showed that cylinder 2 and 3 had the vast majority of misses. 1 and 4 only had a few. I'm thinking I will try a new map sensor and see what happens after that. Any suggestions for any other issues I should be looking at?
 
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I don't know if the Map sensor is ignored in open loop mode, if so that would make sense as to why it runs well cold and wot. At that mileage the o2 sensor could be a bit slow, although in range contributing to the problem.
 
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Apr 17, 2004
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Texas Hill Country
When you use the plugs get the NGK ones or the Delco's from the chevy dealer. I have had good results with my ION and those plugs. Same car as cobalt.
 
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Jun 2, 2002
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Georgia/Retired
Go through the previously mentioned typical tune-up stuff- Clean the throttle body for good measure- Make financial plans to replace the ignition control module- Get the ignition switch recall done- smile
 

FFeng7

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Thank you all for the quick replies. The previous owner stated he did the plugs. I have not actually checked them myself. Perhaps I will get a set of plugs for the car. Perhaps an oxygen sensor too. Is there a particular oxygen sensor that should be replaced first. I believe I have a pre-cat and after-cat oxygen sensor. I also need to get the ignition switch recall done. I had it done on the 2007 Cobalt but not this one just yet. Thank you all again!!
 

FFeng7

Thread starter
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Jun 1, 2004
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Va
Thank you all for the quick replies. The previous owner stated he did the plugs. I have not actually checked them myself. Perhaps I will get a set of plugs for the car. Perhaps an oxygen sensor too. Is there a particular oxygen sensor that should be replaced first. I believe I have a pre-cat and after-cat oxygen sensor. I also need to get the ignition switch recall done. I had it done on the 2007 Cobalt but not this one just yet. Thank you all again!!
 
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I would do the upstream O2 sensor since it does most of the work. The downstream sensor just monitors cat efficiency. New plugs would be a good idea, as well as new plug wires. Go OEM for plugs and wires if you can.
 
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Pull the upstream O2 sensor. See if the car runs better. It will be loud with the sensor removed... If it does run better, your catalytic converter is plugged. If the sensor was bad, it would give you a code (other than the ones you have)
 
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Originally Posted By: mattwithcats
Pull the upstream O2 sensor. See if the car runs better. It will be loud with the sensor removed... If it does run better, your catalytic converter is plugged. If the sensor was bad, it would give you a code (other than the ones you have)
You don't always get a code when an O2 sensor goes. My Silverado had a bad O2 sensor causing one bank to run rich but tripped no codes. I replaced the sensor and never had anymore problem.
 
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Get some delco 41-105 plugs to start. You may have to replace the coil assembly as well. SOunds like what I had going on with my ion.
 
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Oct 24, 2008
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Iowa
Verify the previous owner put the correct plugs in. They need to be iridium. Secondly, the coil boots are old enough that they may allow current to arc to the cylinder head. Those should also be replaced. Pay attention to how they come apart. Replace the fuel filter (this is standard maintenance). Lastly if you still have issues--which I think you may since you have a two cylinder misfire based on your description--investigate the ignition control module. On that platform it should be very near the coils. Do not rev that engine with a misfire. You could cause some bigger problems.
 

ls1mike

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Jun 14, 2008
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In the Garage...
You have that weird one piece coil pack correct? I think you replace the whole thing. I think the boots are serviceable. Could be coils as they degrade when the car warms up. Should be easy to fix. 02, plugs, coil pack you under 200 bucks for parts. Start easy. Plugs and 02 they will need it this age. GM cars will a lot of times not throw and 02 code, even though it is the root cause of the problem.
 

FFeng7

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Jun 1, 2004
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Va
Thanks for all the suggestions. I am going to try some basic tune up items over the next week. I'll keep the board up to date and post some pictures of anything interesting I find.
 
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Sep 23, 2007
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Ignition coil packs are a common failure point on Ecotec engines. Waste spark means that cylinder 1 and 4 spark at from one ignition coil circuit, and that cylinder 2 and 3 spark from the other ignition coil circuit. This suggests to me that you need all new ignition coils and boots.
 
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