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Discussion Starter #1 (Edited)
In the last two weeks or so, my 2006 Cobalt LS 5-speed (all stock, no mods) has started having weird issues with the engine. I got the car in Jan. 2012 with ~125k miles and it now has ~137k miles. When I first got it I swapped the air filter for a K&N filter, changed oil, changed coolant, changed spark plugs (Autolite platinum), and even bought 4 new Michelin Hydroedges (90k mile tires). I even used some throttle body cleaner earlier in the year (along with a toothbrush) to make sure it wasn't gummed up or anything. I change oil regularly (every 4k miles), have recharged the K&N filter at least once, rotated tires a month ago, etc.

Ever since I got it, if I have the A/C compressor on, when I hit the clutch, it'll drop down below 500 RPMs for a second, shudder a little, then come back up to a normal idle, and be fine until I go again, then hit the clutch (due to stop-and-go rush hour traffic).

Now it seems to have lost some power while accelerating (whether slow or highway speeds, all gears). On some days when I start it in the morning (temperatures around 65-75F outside), it will idle between 900-1100 RPMs (not constant, fluctuates back & forth) for a couple of minutes and eventually settle back to a normal idle around 700RPMs. And the problem that only seemed to occur with the A/C on, *sometimes* happens when the A/C is off and has not been turned on since starting the car. Now to be clear: since I've owned the car it has NEVER thrown any codes, stalled due to the A/C or the current issues, failed to go into gear, shifted roughly, or dropped RPMs while accelerating.

I took the car to Midas to check the suspension/steering b/c I was concerned about that. The manager said all of the suspension/steering seemed fine. He did say I may eventually want to replace both front strut assemblies, but that it wasn't needed currently.

Then a few days later I took it back to Midas to also have them check on why the engine was behaving this way. He said the transmission looked fine. He did a test to see if it might be the clutch and said there was no problem there. He had a tech do a road test and found nothing there. He said they checked O2 sensor readings on both sides of the catalytic converter and all was well. He said at this point he would recommend seeing if I had AC Delco plugs since they're tested by GM to work specifically for their vehicles. I thought I had put in AC Delco plugs, but took one out and realized I had the Autolites. Last night I replaced all of the Autolite plugs with AC Delco Iridium plugs. This morning the issue of idling 900-1100 RPMs was still there and it still seemed to not accelerate as much as previously (i.e., a month or so ago). The Midas guy did say that if changing plugs did not correct the issue, his next recommendation would be for them to do a $70 injection cleaning that he said used chemicals better than the normal stuff you get at the stores (I guess industrial strength?)

SO, having said all that, any ideas on what could be causing this issue? Could it be that I need to give it another week or so to see if the problem clears up with the new plugs? Could it be a sensor issue? Something else? And how can I narrow down the list of potential issues?

I previously had a 2000 Saturn LS1 with the same model of 2.2L Ecotec and never had such issues, so I know this ain't normal.
 

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lol damn i just posted about this happening to my car last month whens the last time u got a transmission oil change? mine still does it because i couldnt afford the $179 for the oil change but im hoping to do so soon before anymore damage but i think its called TCC shudder when the transmission randomly locks and unlocks in a gear slight flux in rmp then back to normal i know cause i asked what your asking last month lol coby should be able to explain it better to you because idk all the info but check into that also check out your throttle body too might need to be cleaned.
 

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I guess Bolrae didn't notice yours was manual.

Higher RPM at startup is normal as temperatures get cooler and cooler. Should be around 1200 and settle to about 750. Now for you other problem when pressing the clutch with A/C on... That is usually caused by the sense switch on the clutch and the sense switch on the A/C unit. It is called throttle up. If the "PCM" get's a signal from A/C compressor that it is being turned on it will throttle up to compensate for the extra load, same with fans and steering motor.

In your case I would suspect the A/C pressure switch because if it was sending the proper signal your engine would not dip in RPM when you press the clutch because the "PCM" would already have a throttle flag.

At idle in neutral,parking brake on try turning "ON" and "OFF" A/C to see if engine throttles up or if it bogs down. What should happen is your rpm should go up a bit maybe 200rpm and then settle back down to idle speed. If it just bogs down then your throttle up switch on A/C is not working properly.
 

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Discussion Starter #4
Coby7, awesome! thanks for the info. any thoughts on why I have the issues when the A/C is off... I've had the engine shudder w/ AC on for months, but the engine shudder WITHOUT A/C on is new in the last couple of weeks.


I guess Bolrae didn't notice yours was manual.

Higher RPM at startup is normal as temperatures get cooler and cooler. Should be around 1200 and settle to about 750. Now for you other problem when pressing the clutch with A/C on... That is usually caused by the sense switch on the clutch and the sense switch on the A/C unit. It is called throttle up. If the "PCM" get's a signal from A/C compressor that it is being turned on it will throttle up to compensate for the extra load, same with fans and steering motor.

In your case I would suspect the A/C pressure switch because if it was sending the proper signal your engine would not dip in RPM when you press the clutch because the "PCM" would already have a throttle flag.

At idle in neutral,parking brake on try turning "ON" and "OFF" A/C to see if engine throttles up or if it bogs down. What should happen is your rpm should go up a bit maybe 200rpm and then settle back down to idle speed. If it just bogs down then your throttle up switch on A/C is not working properly.
 

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Bad gas or throttle body dirty again, maybe you sprayed too much oil on your K&N filter and gummed up the "MAF". It could be a million things, hard to tell until you get a code.
 

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I guess Bolrae didn't notice yours was manual.

Higher RPM at startup is normal as temperatures get cooler and cooler. Should be around 1200 and settle to about 750. Now for you other problem when pressing the clutch with A/C on... That is usually caused by the sense switch on the clutch and the sense switch on the A/C unit. It is called throttle up. If the "PCM" get's a signal from A/C compressor that it is being turned on it will throttle up to compensate for the extra load, same with fans and steering motor.

In your case I would suspect the A/C pressure switch because if it was sending the proper signal your engine would not dip in RPM when you press the clutch because the "PCM" would already have a throttle flag.

At idle in neutral,parking brake on try turning "ON" and "OFF" A/C to see if engine throttles up or if it bogs down. What should happen is your rpm should go up a bit maybe 200rpm and then settle back down to idle speed. If it just bogs down then your throttle up switch on A/C is not working properly.
oh lol
 

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Discussion Starter #7
I noticed in the last few days that I'm also having problems when the blower motor is on full, heat is cranked all the way, and fan direction is set to defrost the windshield. Could this somehow be the blower motor that originally seemed to be an A/C problem? If so, how would I tell? Or could it be something else and how could I tell?

I'm sure I could learn to replace the blower motor (via the video below) and my Haynes book, but I'd rather not break the seal and order a factory kit to reinstall the blower motor, especially if nothing is wrong with the motor.

 

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I friend had all sorts of idle issues and lack of power because his intake pipe came a little loose on the throttle body, no codes either. Definitely worth a check
 

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Mine did the same thing, hose clamp wiggled it's way over the TB tube
 
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