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Cobalt

falirayfaliray Posts: 25
edited December 2 in Chevrolet
A few questions. What is normal idle for a Cobalt? I have a 2007 with the 2.2 engine. It used to idle just below 2000 at 60 on the highway. Now it idles just above 2000 on the highway. Is this normal? Its got 158K on the odometer. Ive noticed it seems to be burning more oil and the fuel mileage has gotten worse.

Comments

  • imidazol97imidazol97 Crossroads of America I70 & I75 Posts: 23,887
    edited December 2
    Normal idle is about 750 rpm. That's parked, warmed up.

    I have a 2008 and I'll look when I'm running on level interstate at 60 next time.

    But I'm guessing you're seeing the difference between the torque convert clutch being locked up and not locked up. If you are on level road don't change your accelerator pedal with car going at that speed. Lightly touch the brake pedal just enough it would turn the brake lights on--that should unlock the torque converter clutch to give the engine slightly more revolutions for a little more power and quicker reaction to acceleration, as well as to be ready to downshift if necessary to 3rd gear.

    I'll bet your car does not increase rpm's when you do that. Then you should see the rpm's decrease slightly and smoothly when you take your foot off the brake and especially if you let up slightly on the accelerator but keep it down to keep the engine pulling the car.

    Is your engine warming up properly to 185 deg F according to the digital readout on the dash? Your thermostat may be opening too soon or may be leaking coolant past it and the engine isn't warming up fast enough. If you are in a very cold climate the engine may be operating normally trying to keep the engine warm and provide heat to the heater. See paragraph below.


    Are you in a very cold climate where the transmission might be running colder. IIRC the transmission may not go into 4th gear as early when its oil is cold and the engine is not fully warmed up AND it may not engage the torque converter lockup in 3rd or in 4th under similar cold circumstances. I cannot be sure it does both of those, but I do believe it tries to keep the engine rpm's up some to get the engine warm and operating with less pollution...

    2015 Cruze 2LT, 2014 Malibu 2LT, 2008 Cobalt 2LT

  • imidazol97imidazol97 Crossroads of America I70 & I75 Posts: 23,887
    edited December 3
    In the 4th paragraph, I said that I suspected when you test trying to have the torque converter unlock at a gentle cruise that you will not get an increase in rpms because I suspect your torque converter is not locked up.

    If your thermostat is keeping the engine far below optimum temperature, your should get an engine light or a message in the dash screen telling you that the engine is running too cold.

    If there's something wrong in the transmission that the torque converter is not locking up when the computer tells it to do so, I believe you will get a code and a check engine light. You didn't mention an engine light or a warning in the driver info center where the tire pressures and engine temp and average fuel economy all are displayed along with the oil life used. So I suspect everything is normal.

    Kind of depends on your environment temperature wise and what you find after car is thoroughly warmed and you try to unlock and lock the torque converter clutch.

    BTW, if the torque convert clutch doesn't lock up it makes a small difference in the fuel economy. Not a big deal in most cases.

    AND I did understand that you meant idle at 2000 as in cruising along running at 2000 rpm. I mentioned the normal idle speed in park for other readers who might come across this dialogue.

    2015 Cruze 2LT, 2014 Malibu 2LT, 2008 Cobalt 2LT

  • imidazol97imidazol97 Crossroads of America I70 & I75 Posts: 23,887
    edited December 3
    I may have given you bad information about being able to unlock the torque convert at cruise in 4th gear by touching the brake pedal. That doesn't work on my Cobalt at 60 mph either. The tach at 60 is exactly 2100 rpm. Just slightly below the first mark.

    However, if there's a slight incline up and the cruise control or the accelerator is pressed down, the torque converter allows the engine to speed up 300 or more rpms. Then it smoothly tapers down to 2100. So the torque converter is unlocking to allow more rpms and power temporarily in my car.

    2015 Cruze 2LT, 2014 Malibu 2LT, 2008 Cobalt 2LT

  • thecardoc3thecardoc3 Posts: 5,164

    I may have given you bad information about being able to unlock the torque convert at cruise in 4th gear by touching the brake pedal. That doesn't work on my Cobalt at 60 mph either. The tach at 60 is exactly 2100 rpm. Just slightly below the first mark.

    Just wanted to say, nice job. It takes time to gather information about a system and give good advice. Unless someone worked with this generation of vehicles and specifically this model all of the time they wouldn't know if touching the brake pedal would cause a disengagement of the TCC or not off hand. A tech diagnosing this would rely heavily on data stream, especially the commanded gear ratio versus actual which is a calculation based on the output shaft speed divided by the input. Plus he/she would have to closely monitor the TCC slip rpm desired versus commanded.

    The codes that might eventually set with this one could be;
    P0741 TCC stuck off
    P1811 Max Adaptive, Long Shift (Need to use a scan tool and pull the adaptives to see if the system has to boost line pressure to apply one or more clutches/bands)

    One thing to consider is if the engine is underperforming, that would have the driver open the throttle further to get to a given speed and that could cause the TCC to disengage.


  • imidazol97imidazol97 Crossroads of America I70 & I75 Posts: 23,887
    edited December 3
    Thanks for comments. Always good information that I need to know about my posts, good and bad.

    I used my Autel scanner on my Cobalt and it has no codes. So I assume it is working right and this transmission doesn't unlock torque converter on brake apply.

    I'll have to try my 14 Malibu and my son's 15 Cruze when I have it for service next time to see if they do react to brake pedal or just operate off inputs from the computer controlling them.

    2015 Cruze 2LT, 2014 Malibu 2LT, 2008 Cobalt 2LT

  • thecardoc3thecardoc3 Posts: 5,164
    Look at the TCC slip desired and actual and then change the pressure on the gas pedal and watch the slip change as the TCC releases to allow for more torque.
  • falirayfaliray Posts: 25
    Ok. Wow. Tons of info. Thanks. Yes, I meant when I cruise at 60 mph the tach shows the rpm just above 2000. When I first bought the car it showed just below 2000 at 60.
  • imidazol97imidazol97 Crossroads of America I70 & I75 Posts: 23,887
    My car has 16 inch tires on it. That's the only thing I can think of that might make a difference in the tach speed at 60 mph is if your car has larger tires with a greater circumference and GM didn't use a difference gear ratio to compensate for that.

    My guess is your car is doing fine at 60 mph. Mine has no codes.

    I'd drive it an enjoy it. I like the 2.2 L engine over engines that have a turbo and are smaller. It just seems peppier to drive.

    2015 Cruze 2LT, 2014 Malibu 2LT, 2008 Cobalt 2LT

  • thecardoc3thecardoc3 Posts: 5,164
    faliray said:

    Ok. Wow. Tons of info. Thanks. Yes, I meant when I cruise at 60 mph the tach shows the rpm just above 2000. When I first bought the car it showed just below 2000 at 60.

    It may just be that everything really is normal and the variance you see might not be of any consequence. You can trust that the system is capable of detecting an issue and would generate a fault code and illuminate a warning lamp if one develops.
  • falirayfaliray Posts: 25
    Ok. Ill keep monitoring my car. Thanks for everones answers/help.
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