Question about 2005 Chevrolet Cobalt

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Cobalt engine misfires

I have a 2006 Chevy cobalt with around 53,000 miles on it. I have intermittent misfires, When I start it, my rpms drop down to zero and only have the bells and whistles ( radio, lights etc.) I do not have a check engine light come on. In the past I have had a lean fuel code and the computer was reprogrammed and so far that has been fixed. What could be my problem. the car always starts after a couple of tries and it seems like weather changed affect it, the warmer it is the more often it misfires. please help!!

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  • l_b_townsend Apr 20, 2009

    thank you soo much. this gives me a lot of options to look into. I bought it used about a year ago and have only put about 7,000 miles on it since I bought it last march. I have no clue what has been done to it. I am very good about changing my oil. i have not done any transmission/ coolant/ fuel delievery servies/ flushes since I bought it. I have also not replaced the fuel filter since I bought it, so I dont know when/if it was replaced. I have heard about other problems about ignition problems. I just never connected that because I knew it was a misfire. I just worry that it wont start when I need it to. Thank you for all your help and any other help would be greatly appriciated. thank you.



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I can think of a couple of possible things to check.

When is the last time you put in new spark plugs? Ever? Check them. The problem may simply be worn out spark plugs. Likewise, a bad spark plug cable could cause misfires. Yet that is rather unlikely considering your car's low mileage.

Check the connections of all of the rubber vacuum lines which are attached to the top of the engine and which then are attached elsewhere. A vacuum leak due to loose fitting connections can make it hard to start the car. Likewise a vacuum leak can also cause the lean fuel code since the intake manifold no longer generates as strong of a vacuum as it should.

Virtually all cars have a Positive Crankcase Ventilation (PCV) valve located somewhere on the cylinder head cover. The big rubber grommet around the PCV valve is a common cause of vacuum leaks. Check that the PCV valve is making a snug fit inside of this rubber grommet. While you are at it, pull the PCV valve out of the grommet and make sure that it isn't stopped up. A stopped up PCV valve is very unlikely if you have been good about regularly changing your car's oil.

Check that the clamps for the big hose running from the top of the engine to the air filter housing are snug. And, of course, check that the air filter isn't extremely dirty or stopped up with debris.

It is possible that the mass air flow sensor is defective or has gone bad, but I highly doubt this since your car has very low mileage. Besides, a bad mass air flow sensor on any modern car should produce an error code.

A dirty fuel filter or a weak fuel pump could cause starting problems, and might even cause stalling and misfire problems -- especially when driving uphill. Yet I don't think that this is the problem. Just something to keep in mind as a possibility.

It is possible that the ignition module is either defective or has prematurely gone bad. Usually a good sign of the ignition module going bad is an increasing rate of misfires as the engine gets warmed up. Start the car and let it idle and warm up. If the rate of misfires increases as the engine warms up to normal operating temperature, then it is likely that the ignition module is close to completely giving up the ghost.

Finally, make sure that all bolts connecting the intake manifold and air bell atop the intake manifold are tight. Again, the idea is to get rid of vacuum leaks. This is unlikely, but worth checking. These bolts should never be tightened more than the specified torque values.

Well, these are just some common things which should initially be checked. Assuming that the spark plugs and plug wires are good and considering your car's low mileage, I am betting on either a vacuum leak or a failing ignition module. The latter can be tested by a mechanic who uses an oscilloscope to look for missing ignition module pulses.

Posted on Apr 20, 2009

  • GoneToPlaid Apr 21, 2009

    I don't have a Cobalt, but I did drive one as a rental car two years ago. I think that it was a 2006. I really liked it. Anyway, you might also search online for any 2006 Cobalt service bulletins. Or perhaps try talking to a mechanic at your local Chevy dealership. He might have a really good idea of what the problem is.


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Aveo misfire sometimes when idle or running with the ac on,new spark plugs is installed

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