hey everybody, I picked up my 2007 S/c SS from a dealer about a month ago. Since I got it It has had an idle that sounds as if it is cammed. i now have a ZZP 3" intake and Tsudo exhaust and it sounds the same, just amplified. In addition to idling rough (it does smooth out when the rpm's go up) there's some soot on the inside of my muffler tip, which leads me to believe its running a little rich. i drive somewhat easy and get 250-80 miles out of a tank. The other issue is when the air conditioning is running and i press the clutch in to slow down to a stop the rpms jump from 500 to 2000 for no reason for a moment until it starts idling correctly, err, back to being "cammed." I'll try to get a video up soon, but maybe its a bad sensor somewhere? Again, it did this when the car was bone stock as well, and has not thrown any CEL's before or after installing my mods. Thanks!

 

First clean ur throttle body and maf sensor "just in case"... is ur exhaust full or just cat back??? And are u sure the car is stock??? I thought mine was and it ended up being stage two... And ur gonna need a tune...

 

yea clean ur throttle body (make sure u take it OFF the car, do NOT blow throttle body cleaner into it, if it gets in the supercharger///)

but i have the same kinda rough idle ur talking about when the AC's on. i think its just that a 4cyl can't take all that load honestly

 

The 07's had an idle hunt issue while A/C was turned on.

When I was GMS2, this was a common problem for me.

What tune are you running? Also, the aftermarket intake will exaggerate this idle hunt while the air is on (unless tuned for it).

Below is an e-mail Bill Duncan (GM Engineer) sent me when I had a similar issue....

:: I have more information. The 2007 kit had the hunting idle fixes in it. It had to do with runner cross talk of fuel and A/C loads. it was also sensitive to injector cone angle injector split. Your 42 lb/hr injectors may be the partial cause. Do you know what the cone angle of the pray is and what the split angle is of teh 2 cones on each injector?

Also, any type of vacuum leak would amplify the idle hunt issue. Look carefully for any air leak after the throttle body and try to eliminate it.

Hope this helps,

Bill ::

No.

That is not the problem.

 

Yeah, being a 4cyl isn't the problem.
My car does this from time to time, but my mom's cavy is solid with the a/c on.

 

thanks everyone. Later today I will search for any apparent leaks and get a video up. The car i believe was stock as i got a dyno run done just after I got it. It did 183 WHP and 153 FWTQ. I think those should be about stock numbers, however i was surprised at the torque, low but was very consistent. The exhaust is only a catback for now.

 

Those numbers are very low for a stock pull (Mustange Dyno?).

Stock SS/SC's on average put down 210whp & 185wtq.

 

Wow those are some low numbers...

 

Yeah i thought they were low as well, especially for a front wheel drive car i wasnt expecting 20% Drivetrain loss....thats why i believe something must be messed up. And it was a mustang dyno at EFI Logics in Bethel, Connecticut. Somewhere theres a loss of power going on, just have to figure out what.

 

wtf?? something has to be wrong with the car or that dyno fuking sucks. no way in hell those numbers are possible.

 

If thats EFI logics dyno, ur probably on the mark - that dyno reads LOW. Are the injectors Green? Is the pulley stock? just curious

 

If your in need of some assistance with the issue and a tune, feel free to contact me and I can work something out for ya!

 

Thank you jeremy, I might need to take you up on your offer when I have the money. Sujomatt- Stock pulley and stock injectors. Tomorrow I am trading a fellow cobalt owner in town, giving him my polished aluminum 5 spokes and I get his anthracite. I dont know if this is relevant to the rough idle but occasionally upon startup it sounds like a loose bicycle chain coming from inside the timing chain housing. It does that for about 3 or 4 minutes then goes away. If it was the chain I'd think if would be constant. Could a loose chain lead to a rougher idle???

SOME PICS:

 

That sound would most likely not be related to the rough idle. When was the last time you changed the oil? If the oil is at the proper level and has been changed recently, the noise will probably be from then chain, chain guides or it could be from the tensioner being broken and not pressurizing correctly.

 

I changed the oil about 2500 miles ago, it is full and I use Mobil 1 synthetic. Im convinced something is wrong with the chain.

 

Loose chain allow a cam to skip a tooth?

 

Check ur ic pump high iat2s will make it all worse cuz the stock tunr or s2 tune will start pulling timing lole crazy

 

CLEAN YOUR THROTTLE BODY!!!!!!!!!!!!!!!! i guarantee you it will fix your problem

 

IMG_1909.mp4 video by vinalhaven15 - Photobucket

I took a video with the noise its making. You can hear the miss in the exhaust. Not shown in video is a loud sound that sounds like a loose chain when the rpms are at about 2K.

Changed the spark plugs, thermostat, oil, done all service. Just havent checked I/C pump yet, and still need to check throttle body.

With this noise, it does not begin until the car is driven for 30 plus seconds, and usually goes away after 4/5 minutes of driving. The noise will never start if i start the car and just let it idle, only after it moves.

 

Yup that would be the timing chain tensioner, u need the updated one from crateenginedepot.com

 

as for the ac, its tune, had the same problem, got my tune messed with, now its fixed

 

Once i removed and clean my throttle body my idle issues were GONE. Do that asap as other members have told you....good luck.

 

Threads like these are why this site is awesome. Now lets clear all this up.

When ever you upgrade injectors go ahead and expect the car to idle hunt, if your not upgraded then clean your throttle body and while your at it go ahead and clean your maf. If you are upgraded on the injectors then you can tune it out for the most part.

Your dyno numbers are about right for the dyno you are on, so you dont really need to look for something thats robbing you of horsepower cause your fine.

The rattle noise is what was mentioned above, its your timing chain tensioner. fix it for about 40 bucks and that problem will be gone as well.

All these solutions were mentioned above and are all very normal for these cars. If you serach you will see that there are threads posted like these almost every week with the exact same problems. so I dont know why people come in here with all kinds of crazy ideas thats not wrong with your car.

 

I think his torque is still way too low even for mustang dyno, but follow the how-to guide for replacing the timing chain tensioner so u dont mess up. Check ur ic pump also it could be dead and u not know it.

 

Thanks everyone. I will clean my throttle body and I had a feeling it was the tensioner, but didnt want to believe it because everything on this engine is impossible. (i.e. thermostat) I will try this weekend and post results.

And i did search, but nobody could describe the symptoms i was experiencing. Thanks!