Rough Idle and Rough Stops 09 Cobalt

[Trussell]

Hello

I'm having some problems with an 09 Cobalt LT

After the car has been running and is up to temp, when I restart the car it tends to have a rough idle...it seems to have a misfire but the tach isnt jumping....once the car is in gear it seems to smooth out

Also when coming to a stop, it acts like it wants to stall but so far has not

any ideas what could be the cause? I have done the regular maintenance

Car is a 09 Cobalt LT Automatic with 108,000 miles...its daily driven mostly highway miles

Thanks

[Coby7]

When you say regular maintenance, did you get a throttle body clean at any point? When was the last time you changed the plugs?

[Trussell]

Plugs where changed around around 90,000

Throttle body is next...opps

[Coby7]

Not saying that's what it is but these are notorious for throttle body gumming up. Once you clean that black tar like stuff it will run just like new.

[Trussell]

One more question

Is the throttle body near the air filter box or at the front of the motor?

[Coby7]

Yes, right at the front under that big cover. If you look at pictures of N/A with cold air intake you can clearly see the throttle body.

[Trussell]

Thank ya

[johnccc]

I had this exact issue, I repaired it myself when I almost got into many accidents due to the car turning off sometimes.

I cleaned the throttle body and changed the air filter.

You can remove the throttle body from the motor, clean it up with carb cleaner, you can reuse the seal, its rubber, feel free to buy another one if it makes you feel better, there not expensive.

You can test if its the throttle body easily;

1. Start your cobalt.
2. Rev it up to about 3000 revolutions, hold it for a few seconds.
3. Release the gas pedal completely.
4. Observe the Revolution needle as it returns to idle.

Test is complete.

If you rev counter drop rapidly when you released the gas, clean your throttle body.

If it went down slowly, then it could be something else.

Your MAF sensor could also be dirty/broken, this can cause rough idle and bad shifting, try cleaning that too, its the sensor that is right after the air filter, very easy to get to.

Try these one at a time.

[jignaczak]

the sticking throttle body would cause this issue,

Also, you could have an issue with the pedal module... I used to see it all the time when I worked for saturn on the ions and vues

[BillBurger09]

Mnedoes the same thing, it'll just randomly bog from idle to about 450-500 RPM. It dosnt completely stall, but it probabl would if i didnt catch the idle with the gas pedal...