Idle/High RPM/MPG Problems - Chevy Cobalt Forum / Cobalt Reviews / Cobalt SS / Cobalt Parts
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post #1 of 6 (permalink) Old 05-02-2011, 10:09 AM Thread Starter
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Idle/High RPM/MPG Problems

ok so i have a 2007 chevy cobalt ls 5 speed. for my graduation project i decided to build a custom cold air intake, since i read a lot of people had completed it succesfully. so i put it on. i also cleaned the top of my throttle body, i didnt take it off the intake manifold but i did spray a rag, and then wipe everywhere i could inside. and yes i moved the part that opens and closes. i put a cone over my PCV valve where there used to be a vacuum line from my valve cover to my intake tube.
PROBLEMS:
-idle feels jumpy, when just sitting there it feels almost as if the engine loses some power for a split second, but then jumps right back, it has vibration when this happens. this occurs about ever 3 seconds at idle
-i have the famous high RPM problem now. if im driving and shift out of a gear and into neutral, my RPM don't drop like they're supposed to. they just stay up. sometimes when i come to s complete stop my RPMs are still around 2500 - 3000 and then they start to fall. i idle at about 1000 RPM
-last, since i did this intake, my MPG has gone down to about 20 - 24 MPG. this is about 3 MPG worse then what i got with my stock intake on.
I HAVE TRIED...
-unplugging both battery terminals for over an hour and a half
-the whole TB "reset" where you turn your key to ignition, not on, for 30 seconds
-i dont have any leaks on my intake, i checked
-Ive cleaned my MAF sensor with the crc cleaner, so its not dirty.
-The arrow is pointing towards the throttle body when installed in my intake.
-I changed my spark plugs

Please if you have any ideas let me know ASAP! this has been happening for about 4 days now. thanks guys, please help me out
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post #2 of 6 (permalink) Old 05-02-2011, 11:42 AM
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the computer relearned idle position. only fix (that i have found that permanently works) is to reflash the ecu. dealership can do this in about an hour. costs very from dealership to dealership but should be anywhere from 50-100. and yeah, my gas mileage went down when i installed my k&n. more air = more gas I guess.

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post #3 of 6 (permalink) Old 05-02-2011, 06:49 PM
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same problems

Hi, i have the same problems. also a 07 ls auto its like my car has cruise control now lol, just wondering when flash the ecu does it get rid of the idle jump when your stop in gear?
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post #4 of 6 (permalink) Old 05-03-2011, 05:09 AM Thread Starter
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im not sure whats going on. i tried the idle relearn procedure and that didnt do anything. i dont know what else to try. so im taking it to the dealership today to get the ecm flashed, since thats the only solid solution im seeing. ill let you know how it works

if you want to try this, im sure it wouldnt hurt. the idle relearn procedure is, disconnect both battery terminals for 5 mins. then start your car and let it run for three minutes, then turn it off for one. repeat the starting and stopping procedure three times. (you dot need to disconnect your battery after the first time.)
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post #5 of 6 (permalink) Old 05-03-2011, 05:48 PM
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ya i've tried the relearn an no difference i've even loosened the tb an retorqued it an no difference. hopefully the flash works.
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post #6 of 6 (permalink) Old 07-18-2011, 01:35 AM
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When I had an Alero it would do this same exact thing. Thought it might be the fuel pressure regulator so we changed that. Turned out to be a hole in a vacuum line going to the throttle.. Check all the vacuum lines before spending a lot of money!! $3 fix!
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