By on February 27, 2013

Brandon writes:


I own a 2010 Cobalt SS and I’ve been having random problems with it. I’ve tried checking the forums and I haven’t found any information that matches my car’s problems. It seems like most of the posts on the Cobalt SS forums are by people with modified/tuned cars, and mine is completely stock.

I’ve had a few problems fixed under warranty, but the random problems I’m referring too are ones that apparently haven’t thrown codes. Since the car is still under warranty, I’ve been to 2 dealerships and both dealers claimed they couldn’t replicate the problems. One dealership refused to open the motor up without seeing a code. The other claimed that they took the cylinder head off and checked the intake manifold, but couldn’t find anything. (I don’t trust that they did this)

If you and the B&B have any ideas about what might be causing the problems, I might be able to point a dealer’s mechanics in the right direction and get them to take another look. The next time one of these problems happens, I’m going to bite the bullet and go get an OBD-II scanner to see if I can figure something out. The codes don’t always lead directly to the problems though…

The problems: Sometimes after a rain or letting the car sit for more than a day or so, the idle will be very rough. The revs will jump around and the car will vibrate heavily and rock sideways. This problem clears up after letting the car idle for a minute or so, or after driving it cautiously by using light throttle and keeping the revs below 2500. This problem is bizarre: the car feels like it has a small block with a thumper cam, but the exhaust note is steady, there’s no smoke, etc.

At random intervals, the car will shake badly after I shift into first and get the car moving. The shaking is front to back, not sideways, and it feels like the engine isn’t firing properly and might stall. This shaking occurs at up to 2000 rpm or so. Revving higher than that clears it up. I’ve read that DI motors sometimes experience light throttle/RPM driveability problems, so I’m wondering if that’s what I’m experiencing. This problem also occurs after start up only.

On three occasions, the engine has backfired badly. After each upshift, the exhaust would emit a series of loud pops. There was no smoke from the exhaust and nothing came out of it so far as I can tell. The backfires would stop after shutting the engine off or just driving around normally for a few minutes. This problem is hugely amusing when it happens, but worrisome because it obviously shouldn’t be happening.

For completeness’ sake, the engine problem I did have fixed was a melted emissions line. The line was replaced and heat shielding was added to prevent further occurances. That was 33k miles ago, and the problem has not reoccurred so far as I can tell. Other problems were things like brakes, bad ignition module, etc. that have nothing to do with the engine or transmission.

Finally, the transmission is giving me problems. The transmission will randomly not let me put the car into a gear. As I go to shift, the gearbox will refuse to let me slot the stick into gear. If you’ve ever driven a car with a shift lockout, that’s what it feels like. (The car has no shift lockout though) It happens regularly with first through third, but reverse is really bad. Pushing and releasing the clutch usually cures the problem, but on a few occasions I’ve just turned the car off and walked away because I couldn’t go into reverse. I rarely shift above 3500 rpm, but these days, it feels like I’m forcing the car into gear when I do so. So…master cylinder going bad? Synchros dying?

Frankly, the random problems that are cropping up make the car feel like it will be a huge liability after the warranty expires. If I can’t get this stuff diagnosed and fixed, I may dump it and accept the financial hit. All of the maintenance has been done on or ahead of schedule. To try and prevent carbon buildup on the intake valves or in the turbos, I’ll do full throttle on the highway 2-3x a month and follow that with at least 25 minutes of further highway driving. I also won’t let the car hit boost and then immediately shut it off, also to prevent turbo sludging.

I rolled the dice on GM once before with a Monaro/GTO, and that car was perfect. The Cobalt doesn’t feel like it’s going to go the distance, and that’s a shame because it’s a blast to drive.

Sajeev answers:

I really hope there was a miscommunication between the mechanic, the service advisor and yourself: pulling the head and checking the intake manifold is like a doctor cracking open your skull to get a better look at your deviated septum. It’s fun to be a clueless armchair quarterback!

Now it’s possible the mechanic took the head off to check for coking problems commonplace in direct-injection engines, but I find that hard to believe: a borescope should do the trick for much less labor.  Then again, if GM’s warranty is paying for the labor…but that’s not the point.  I suspect you need to blow the carbon out of your little DI mill.  Run that little thing all the way to redline a few times: it’s the nature of the beast.  And it’s been that way since the Mercedes 300SL I drove many moons ago.

The transmission?  Perhaps the hydraulic clutch assist is bad in some manner (bad cylinder, a leak, cooked fluid) or perhaps a switch to a different transmission fluid is in order.  I’m guessing you need to flush the clutch fluid: if it is even remotely smoky or discolored, flush it out.  I suspect that will fix the problem.  The heat generated from a turbo mill can easily cook that fluid…it’s entirely possible.

Is this a good reason to dump it when the warranty expires?  Provided my repair guesses are correct? Nah, probably not.

Off to you, Best and Brightest.

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37 Comments on “Piston Slap: Feelin’ Blue, Cobalt?...”

  • avatar

    Probably won’t help, but at least gives you something to do: clean the mass airflow sensor. Clean the intake manifold. Inspect the mass airflow wire harness.

  • avatar

    These sound like firing order problems. I hesitate to second guess something this simple to diagnose from my desk, yet your description of an ignition module change makes me suspicious. Those are fun little cars, but if you’ve owned it from new and these quirks cannot be ameliorated, I would be concerned, too. You shouldn’t have to make multiple trips to the dealership to have this car run and shift correctly. Everything I buy has a six-month teething period while I iron out the kinks, but that is the price paid for buying used. My wife thinks I change cars so often just so I can play mechanic. She is probably right.

    • 0 avatar

      Also sounds like a timing issue to me. I’ve slipped a tooth or two on a timing belt job and experienced something similar. Except that it was all the time, throughout the rev range, pretty much. But an older Nissan Hardbody pickup.

      Since this is a VVT engine, and the problem’s intermittent, I’d suspect a computer issue. A faulty computer might also be why it’s not throwing any codes.

  • avatar

    The rough idle after sitting or rain sounds like condensation of some kind to me. The metal cools and attracts moisture, when the part gets hot the condensation evaporates and things go back to normal. I’d make sure all the various connections under the hood are tight and maybe hit them with some electriclean.

    The transmission issue sounds like the clutch not fully disengaging. maybe its fluid, maybe its a mechanical thing. I’d make sure it is adjusted right and that there are no bubbles in the lines.

    That’s it from my part of the peanut gallery. That’s a kickin’ little car, though. I could go out and make get in some real trouble with it.

    • 0 avatar

      The Car Talk answer to a rough idle after sitting in the rain is often sparkplug wires.

      I don’t know if it applies in this case, but it’s a possibility to consider.

      • 0 avatar

        It applies to ignition coils in the same manner. Over time, they can develop a crack and when the conditions are just right, leak spark or just not fire a spark.

        I have one going out right now on my xB. It’s quite common on all makes and models. It’s impossible to pinpoint which coil when it’s not misfiring. I’ve tried spraying them down with water to get it to happen to no avail.

        The transmission thing sounds like a clutch adjustment. Trying to force the car into gear will kill all the synchros, so depending on how long he’s been doing that, he may need some trans work as well.

        • 0 avatar
          bumpy ii

          Buy one new coil and replace the old coil at one end of the engine. If the problem comes back, swap the #2 coil for the one you took out of #1. Repeat as needed.

          • 0 avatar

            Agreed. If rain is a factor it’s ignition. Try running the car and spraying each coil with water. If one starts arcing or the engine starts to run rougher when you hit it there’s your problem.

      • 0 avatar

        Reminds me of the MkIV Golf I used to drive (and park) at the train station.
        On wet days, starting it was a pain, and it would be in the dangerous “limp mode” where it won’t go over 2k rpm (and even that, it takes eternity to reach)

        Could it be a similar issue?
        I understand MkIV Jettas/Golfs had problems with ignition coil packs etc.

  • avatar

    Cold start:

  • avatar

    1) Cheapest OBD scanner solution: ELM 327 bluetooth OBDII dongle for 17 $ + Android Smartphone + Torque App.
    2) Wild guess for the shaking in idle: engine coolant temperature sensor. Leaky casing -> soldering gets wet in wet climate and reports wrong data -> mixture not rich enough -> bad manners.

  • avatar

    Try and reproduce (cold engine) at night and open the hood and see if there are any sparks jumping around. I assume coil on plug so you may have a plug that is grounding out (and no wires in the traditional sense). Also, reseat your fuel injector connections and recheck the connections at the spark plugs. It is possible they didn’t put any dielectric on them at the factory. I am also thinking a flaky cam sensor (air gap?)could play into this or connection.. Lastly.. get a spray bottle with water and mist it around the engine bay to reproduce.

    I know it’s relatively a newer late model vehicle, but do not assume they did everything correctly at the factory. Worst case, throw a flight recorder on it if you get nowhere.. and request one if you get the run around again.

    Good luck

  • avatar

    As a 2008 Cobalt SS owner, I question the validity of some of the information reported by Brenden. These cars DO have a reverse lock out. The fact that you don’t know this either worries me that you are a clueless owner or there is something wrong with the shifter/cable adjustment. However, I would think that something being that wrong would prevent you from ever selecting a gear.

    In terms of Sajeev’s suggestion to change to a different transmission fluid…DO NOT DO THIS! There is only one manual transmission fluid approved for this vehicle and is good for the life of the vehicle. I changed mine at 50,000 just to be safe, but it was like $25 for 2 quarts at the dealer (this is the only place I could locate the specific kind necessary).

    For the record, I have not had any major issues with my car. They are so much fun to drive and I encourage you not to give up on yours!

  • avatar

    There’s no excuse for not having an OBDII scanner. While they are very overpriced at auto parts stores, and, curiously, Harbor Freight, you can get one from Amazon for about $20. They are very basic (all of two buttons) and won’t talk to anything but the ECU, but if all you need is to set or reset engine codes, it’ll work great.

    In any csae, when my car had a similar problem, which caused the CEL to blink one morning, the dealer also had a bear of a time finding it. Luckily it was throwing a code for a cyl. 2 misfire (but not bad enough for a CEL.) The mechanic moved around plugs, coils, and injectors and procto-scoped the cylinder. The problem turned out to be a short in the wiring harness heading back to the ECU; he patched it up and he problem hasn’t returned for the 8 years since this was done.

  • avatar

    I had a similar problem with rough-idle with a Jetta. Ended up being the ignition module. It was cracked, letting in moisture, and after it rained, or sat around a bit, it caused quite some problems. Actually happened twice.

    Problems sound like they’re stemming from that system. You need to invest in a scan tool and plug it up when the car acts up. See what misfire codes you get. On the Jetta, I had random misfires over all the cylinders.

    I doubt carbon buildup is a problem. But, we have a new V6 Mustang with DI. Every time I change the oil I get a can on intake/throttle body cleaner. With the engine idling I slip the straw of the can under the intake hose and, in spurts, run the can through the intake.

    As far as your transmission goes….. Check the clutch-cylinder fluid, maybe check the cable. I see a lot of “hard to shift” complaints and it usually comes back to the person just doesn’t know how to work a manual. Don’t want to be mean, but that seems the case, or they per-maturely fry the clutch or screw the synchros, because once again, they can’t drive a stick.

  • avatar

    You dont always need a code for this type of diagnosis.
    Have your technician use his scanner to access “OBD II Test Modes”, specifically “Mode 6″(Diagnostic Monitoring Test Results). Then view “Missfire Counts”. If there is a missfire that will not set a code, you will see one cylinder with a number higher than the others.
    In any case, I would DIAGNOSE the issue before any parts are replaced or any procedure is performed.

  • avatar

    You have an ignition problem.

    The only reason the mechanic pulled the head was to make some warranty money for the shop – that was totally unnecessary.

  • avatar

    Tip: Put the problem in the first paragraph, not half-way through the letter. It’s wise to get to the most important info as soon as possible since people will stop reading if they lose interest.

  • avatar

    As a previous Cobalt SS owner, (Supercharged, not Turbo) I also had a hitching and lurching problem during and after a rainstorm. The culprit? The air filter. It was positioned in such a way that it would get soaked while driving in the rain, and would take a day or two to dry out and provide good airflow again, (during light acceleration it was not an issue; only when I gave it the beans would it hitch and lurch when the filter was still damp). In time I deduced that it was actually getting soaked by the mist of the cars in front of me WHILE driving in the rain, as the air filter is located ahead of the left front wheel, very low to the ground. So I learned to back off from traffic during wet weather, and that did help. I also had a complete stall and restart occur while accelerating onto a highway on-ramp. That turned out to be something called a barometric pressure sensor. Good luck!

  • avatar
    Mr Imperial

    I also recommend a thorough check of the entire ignition system. Personally can vouch that ignition wires with cracks, cracked coil-on-plugs (also check the wiring to the coil-on-plug for chafing/exposed wire) can cause those same symptoms.

    Where is the car at mileage-wise? Are the original plugs still in it? Might as well check at this point, pull plugs and inspect.

    Tranny-start off simple-where is the fluid level at, and what is the color?

  • avatar


  • avatar

    “Backfiring” out the exhaust is when a combustible mixture leaves the engine and burns (explodes) with a pop in the exhaust system.

    On any modern car, this has got to be a missing spark; IOW, an ignition problem. Not to say that ignition is the source of all your troubles; you may have multiple problems. But ignition is definitely one of them.

    I urge you to invest in an OBD-II scanner. There are distinct codes for “cylinder 3 misfire” (for all cylinders) in OBD-II, and many (all?) modern FI systems will *try* to pinpoint exactly what cylinder has the problem. They’ll usually be wrong, but I suppose that’s part of the charm. :-)

    Start by fixing the ignition problem and then see what else is wrong.

  • avatar

    I doubt it’s carbon buildup, although that’s always a possibility on a DI engine. From what I understand Sajeev’s “run it fast and hard” fix won’t help, as the gasoline in a DI motor never touches the intake valves.

  • avatar

    On the shifting thing, try pumping the clutch pedal several times before shifting into first. If this fixes the problem there’s an issue with the hydraulics.

  • avatar

    Next time you’re in for servicing, ask if your powertrain has the latest calibration revision for the MY/Trim of your Cobalt. That is where I would start. Changing the clutch (is it shared with the brake reservoir?) fluid is a easy win. Judging from your knowledge, I would pay someone else to do this. Cold starts are a bitch – check your air intake. Check your ignition systems (misfires can be read by a scanner).
    Look on forums, find a different dealership. I worked at a Goodwrench and they were top notch. Good service departments are hard to come buy.

    I thought the injectors on the ecotec DI’s hit the valves, but I could be mistaken.

  • avatar

    I would dump it. These are the types of problems that can take months to diagnose, and even then you would have to get lucky with a good smart mechanic, the problem is not easily duplicated, and could be very serious. Sounds like the dealer is clueless, I bet the forums are pretty useless with this too. These cars are not known to be unreliable, so it sounds to me like you have a lemon. Cut your losses and move on.

    Once the warranty is out you will be spending big money chasing the problem down and possibly never fixing it. If you try to sell it then, it will be too old to get good money for it. If its still under warranty then you can probably sucker a good trade value for it on something new.

    Mazda is having trouble moving the Mazdaspeed3, VW always has GTIs on sale, the Veloster Turbo is getting good reviews, the new Focus ST is nice, etc. There is no shortage of FWD turbo cars out there these days that will be as fun as your Cobalt. Or just buy another Cobalt SS, they are bargains in the used market and I doubt you will have the same problems again. Or try something new and look at a Mustang or Civic Si or FRS.

  • avatar

    Sorry to hear about the Cobalt issues. I’ve not read all the comments, but from what you describe that is just plainly frustrating. By this point I’d start checking into my states lemon laws and see if you can get rid of the car.

  • avatar

    Release baring on your clutch is bad. Front to back shaking and difficulty getting into gear is a dead giveaway. With cold stats, If you start the car, clutch in and in first gear that could explain your cold start issues to because the clutch is not fully disengaged.

  • avatar

    First off, take advice you get on the interwebs with a grain of salt- we haven’t inspected or driven your car and can only throw you a few possible culprits. If you aren’t knowledgeable about the workings of cars, you can’t evaluate them. This applies to the following as well. Start with the simple. The “Italian Tune-Up” is a starting point (WOT operation), as much as you can (semi-)legally achieve. Secondly, after a rainstorm, dismantle and inspect the intake tubing and air cleaner housing. My bet is you will find standing water somewhere in there. A few strategically placed small drain holes can work wonders. Regarding the clutch, Sajiv recommended changing the clutch hydraulic fluid. I would start with a simple bleeding of the slave cylinder. If that improves things, then a fluid change will probably also help. I think your car may use the brake fluid reservoir to feed the clutch master cylinder. Brake fluid needs to be changed every two years anyway, so you will kill two birds with one stone.

    I am amazed that people will neglect maintenance on their second most major purchase, then sell it in fear of a breakdown from that neglect. A well maintained car should last ~15 years. Someone above misread Sajiv’s advice to change the clutch fluid as changing the transmission fluid. That “lifetime” fluid does need to be changed, but not for a few years yet. And yes, substitution is ill advised.

    • 0 avatar

      Be careful where you drill holes in the intake system….unmetered air entering the engine after the MAF sensor will totally whack things up….the last thing you need to add to your woes. I agree with ignition being your first problem. Damp weather and unburied fuel in the exhaust tells me that you are getting misfire. Now misfire that bad on a GM should set your mil blinking in a hurry. I suspect that you have multiple misfires and a reason for the ECM not seeing the misfire. I believe the misfire is detected by crank position sensor seeing the crank in slightly different position because of the misfire… I would suggest a bunch of the other suggestions already posted in this order: hook up a scanner and try to catch the data stream freeze frame. This should show the misfire and it might pinpoint the cylinder. If not the check for nighttime sparks with water and swapping the ignition coils to try to move the problem. Then I would figure out why you did not register the misfire. Frankly, rom the amount of poor running you speak about I find it hard to believe the ECM didn’t catch any of it. That is perplexing….

  • avatar

    I have spent thousands of dollars, on many many cars, dealing with intermittent problems. Get rid of it.

  • avatar

    It’s the simple things that get overlooked. Like a loose or rusting ground strap, engine block to body.

  • avatar

    Kind of a shot in the dark but, check plugs for gap…have the car outside, preferably COLD. Check compression. Turbo Saabs with similar engines have had intake valves with insufficient heat-treating “chamfering” causing the valve not to seal properly when cold, but the problem seems to go away after warm-up.

  • avatar

    OP said: “To try and prevent carbon buildup on the intake valves or in the turbos, I’ll do full throttle on the highway 2-3x a month and follow that with at least 25 minutes of further highway driving.”

    Sajeev said: “I suspect you need to blow the carbon out of your little DI mill. Run that little thing all the way to redline a few times: it’s the nature of the beast.”

    Unless a Cobalt SS has dual port and direct injection, the so-called “Italian tune-up” shouldn’t do anything here re: carbon on the intake valves. You need to run Seafoam or something similar in the intake to get rid of the carbon.

    The Italian tune-up works for port injection when there is fuel washing the intake valves, but AFAIK doesn’t work for DI, unless the DI engine has dual injection. The fuel is never washing the intake valves, as it is in port or dual injection.

    What’s happening is that the PCV system is sending gunk to the intake, which deposits as carbon on the intake valves. No amount of extra fuel will get this out because the fuel never hits the intake.

    The alternative to Seafoaming is to disassemble and physically remove the carbon.

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