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post #1 of 7 (permalink) Old 10-19-2013, 05:49 AM Thread Starter
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Idle Not Dropping Completely

08 Cobalt 2.2 manual

My regular idle is roughly 800 rpm, but every so often it likes to hang at 1200 rpm. It isn't a constant thing, and it seems to be completely random. Warm/cold, whenever. I'm thinking IAC, maybe it needs a cleaning?
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post #2 of 7 (permalink) Old 10-19-2013, 06:06 AM
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It could be your idle air controller if your Cobalt had one.

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post #3 of 7 (permalink) Old 10-19-2013, 06:18 AM Thread Starter
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It's funny you should say that, because I wasn't entirely sure whether it had one or not. My last two vehicles did, and when I googled the Cobalt, I was under the impression it had one. My mistake, thanks for your help.

Ed; throttle actuator control module, eh? I wish I didn't have drive by wire, and electric assist steering.

Last edited by theroadvirus; 10-19-2013 at 06:22 AM.
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post #4 of 7 (permalink) Old 10-19-2013, 08:57 AM
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Yeah, combination of Accelerator pedal position sensors, throttle position sensors (2,2L has 2 built in the throttle body and are non serviceable) MAF, MAP and IAT sensors. When it works it works very good not so much when one of these fails or gets out of specs.

---------- Post added at 12:51 PM ---------- Previous post was at 12:47 PM ----------

Maybe it's just a bit of carbon and residue stopping your butterfly from coming to it's detent idle position. Have you tried cleaning your throttle body. (Make sure key is out of ignition to do this.)

---------- Post added at 12:56 PM ---------- Previous post was at 12:51 PM ----------

ECM will try 3 times to bring it to detent position with 3 seconds intervals when it sees APP is at idle position. (This is call Ice break mode) After it will try to match idle mixture for whatever throttle position it reads

• Ice break mode--If the throttle blade is not able to reach a predetermined minimum throttle position, the ice break mode is entered. During the ice break mode, the ECM commands the maximum pulse width several times to the throttle actuator motor in the closing direction.

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Last edited by Coby7; 10-19-2013 at 12:05 PM.
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post #5 of 7 (permalink) Old 10-19-2013, 10:04 AM Thread Starter
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I tried cleaning the throttle body as best I could with a toothbrush and some throttle body/maf cleaner. I used to do this as a co op student years ago at Chrysler and it seemed to work better, but oh well. it started pouring so I cut it short. Right now it isn't doing it, but it wasn't happening all of the time anyways, so I'll have to drive it a bit and see.

One thing I was curious about, and after reading your reply, it may reference this. The throttle plate doesn't actually sit in the full closed position (I can push It flush with my finger). Is this how it allows air through for idle, without an IAC?

Pre-clean:


Post-clean:


Throttle plate fully closed:



Oh, and one other question, what's the idle on a 2.2 Ecotec in a Cobalt supposed to be?

Last edited by theroadvirus; 10-19-2013 at 05:56 PM.
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post #6 of 7 (permalink) Old 10-19-2013, 12:06 PM
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The engine control module (ECM) is the control center for the throttle actuator control (TAC) system. The ECM determines the driver's intent based on input form the accelerator pedal position sensors, then calculates the appropriate throttle response based on the throttle position sensors. The ECM achieves throttle positioning by providing a pulse width modulated voltage to the throttle actuator motor. The throttle blade is spring loaded in both directions, and the default position is slightly open.

---------- Post added at 02:17 PM ---------- Previous post was at 02:12 PM ----------

Quote:
Originally Posted by theroadvirus View Post
Oh, and one other question, what's the idle on a 2.2 Ecotec in a Cobalt supposed to be?
When warm it depends if you have the clutch depressed or not but in neutral with no clutch depressed it should be between 750 and 800rpm with no A/C and not touching the steering.

---------- Post added at 04:06 PM ---------- Previous post was at 02:17 PM ----------

Found that mode....
• Ice break mode--If the throttle blade is not able to reach a predetermined minimum throttle position, the ice break mode is entered. During the ice break mode, the ECM commands the maximum pulse width several times to the throttle actuator motor in the closing direction.

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post #7 of 7 (permalink) Old 10-29-2013, 04:30 PM
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There is no IAC on drive by wire cobalts, it uses the throttle body entirely to adjust the idle, typically you will see about 14-18% on your "TPS" which is actually the numerical value for the throttle motor position, which is why you will only ever see 88% at 100% accelerator position.

Try the idle relearn procedure, i had to do this when running a LSJ throttle body and vice versa. Key on and off 3 times and then start the car on the 4th turn of the key and let it idle for 90 seconds, this should fix your issue. I had a similar issue with the LSJ throttle body swap on my LE5. When you started the car it would idle down fine, if you shifted into drive or reverse it would idle fine, but if you revved the car up in the neutral or park position, it would hang up at 1200rpm.
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