Idle Behavior -- Modded LS2
Thread Starter
Racer
Joined: Nov 2006
Posts: 448
Likes: 0
From: Dallas, TX
Idle Behavior -- Modded LS2
Hi all,
I've been having an annoying problem with my '07 C6 and was hoping to get some insight into what I should investigate. Here's what happened:
Last summer I had a mild cam and headers installed, then re-tuned.
After a few months, I started having intermittent idle problems where it would raise up to about 1500 RPM and stay for 10 seconds (maybe longer), then back down to a more normal 800 RPM. I don't believe that it flares up when the engine totally cold, but pretty much always does it when I start the engine when it's still warm -- and the problem does not go away after that point.
I did do one HPDE track day prior to the problem starting but doubt that had anything to do with it.
It seems to happen in warm and cool weather as well -- I thought it might have been a tuning problem with cold weather as fall coincided with the problems starting, and it was tuned in Texas heat.
Thoughts?
Thanks in advance. See sig below.
I've been having an annoying problem with my '07 C6 and was hoping to get some insight into what I should investigate. Here's what happened:
Last summer I had a mild cam and headers installed, then re-tuned.
After a few months, I started having intermittent idle problems where it would raise up to about 1500 RPM and stay for 10 seconds (maybe longer), then back down to a more normal 800 RPM. I don't believe that it flares up when the engine totally cold, but pretty much always does it when I start the engine when it's still warm -- and the problem does not go away after that point.
I did do one HPDE track day prior to the problem starting but doubt that had anything to do with it.
It seems to happen in warm and cool weather as well -- I thought it might have been a tuning problem with cold weather as fall coincided with the problems starting, and it was tuned in Texas heat.
Thoughts?
Thanks in advance. See sig below.
Last edited by DannyBoyC6; Mar 5, 2012 at 05:11 PM. Reason: Corrected info
Thread Starter
Racer
Joined: Nov 2006
Posts: 448
Likes: 0
From: Dallas, TX
Thread Starter
Racer
Joined: Nov 2006
Posts: 448
Likes: 0
From: Dallas, TX
No luck finding an O2 sensor / wiring problem. No melting anywhere that I can see, and the sensors themselves "look" OK to me.
Anyone else have any ideas on what to look at? Could a vacuum leak cause this? What about the tune (it was good when I picked it up from the tuner, so I can't imagine it could "float" out of whack after months)? MAF sensor?
Thanks
Anyone else have any ideas on what to look at? Could a vacuum leak cause this? What about the tune (it was good when I picked it up from the tuner, so I can't imagine it could "float" out of whack after months)? MAF sensor?
Thanks
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
My very first thoughts were VACUUM LEAK. That can make the idle behave badly. Go over EACH vacuum line and connection and make sure that ther sound!! Also, make sure that the ducting from the MAF to the TB is air tight. If all that looks good, spray some brake parts cleaner around the intake manifold and inaccessible areas. If the idle changes, there’s a vacuum leak there.
One other thing is it could have a dirty MAF. Remove the MAF and spray it out with MAF cleaner, let it evaporate and reassemble. While its apart, clean the Throttle Blade.
One other thing is it could have a dirty MAF. Remove the MAF and spray it out with MAF cleaner, let it evaporate and reassemble. While its apart, clean the Throttle Blade.
Thread Starter
Racer
Joined: Nov 2006
Posts: 448
Likes: 0
From: Dallas, TX
My very first thoughts were VACUUM LEAK. That can make the idle behave badly. Go over EACH vacuum line and connection and make sure that ther sound!! Also, make sure that the ducting from the MAF to the TB is air tight. If all that looks good, spray some brake parts cleaner around the intake manifold and inaccessible areas. If the idle changes, there’s a vacuum leak there.
One other thing is it could have a dirty MAF. Remove the MAF and spray it out with MAF cleaner, let it evaporate and reassemble. While its apart, clean the Throttle Blade.
One other thing is it could have a dirty MAF. Remove the MAF and spray it out with MAF cleaner, let it evaporate and reassemble. While its apart, clean the Throttle Blade.
I'll definitely clean the MAF and blade tonight just in case.
Thanks again
Racer
Joined: Dec 2010
Posts: 418
Likes: 0
From: South Central Kansas
Not only the vacuum line at the throttle body, but the throttle body mounting and associated air tubes. Remember vacuum starts at the throttle blade and can leak anywhere from there to the intake port at the cylinder head. That makes it necessary to check everything in between. Also check the vacuum hose at the brake booster and for good measure make certain the intake manifold bolts are tight. As another poster stated spray brake parts cleaner or carb cleaner is good to use when checking for vacuum leaks, when the cleaner is sucked into the vacuum leak the engine will slightly change rpm.
Last edited by 1fastbob; Mar 6, 2012 at 01:28 PM.
Thread Starter
Racer
Joined: Nov 2006
Posts: 448
Likes: 0
From: Dallas, TX
Not only the vacuum line at the throttle body, but the throttle body mounting and associated air tubes. Remember vacuum starts at the throttle blade and can leak anywhere from there to the intake port at the cylinder head. That makes it necessary to check everything in between. Also check the vacuum hose at the brake booster and for good measure make certain the intake manifold bolts are tight. As another poster stated spray brake parts cleaner or carb cleaner is good to use when checking for vacuum leaks, when the cleaner is sucked into the vacuum leak the engine will slightly change rpm.
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Drifting
Joined: Feb 2010
Posts: 1,527
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FYI. Free internet information is not Gospel, need to take it with a grain of salt from "Experts".
Brake cleaner is highly flammable, spraying indiscriminately on an running engine is unsafe, catastrophic with an unintended spark and is detrimental on rubber parts nor friendly to electrical components around engine compartment. Use can do more harm than good.
Chemicals have unique application. Read manufacture's directions and warnings.
Brake cleaner is highly flammable, spraying indiscriminately on an running engine is unsafe, catastrophic with an unintended spark and is detrimental on rubber parts nor friendly to electrical components around engine compartment. Use can do more harm than good.
Chemicals have unique application. Read manufacture's directions and warnings.
Racer
Joined: Dec 2010
Posts: 418
Likes: 0
From: South Central Kansas
FYI. Free internet information is not Gospel, need to take it with a grain of salt from "Experts".
Brake cleaner is highly flammable, spraying indiscriminately on an running engine is unsafe, catastrophic with an unintended spark and is detrimental on rubber parts nor friendly to electrical components around engine compartment. Use can do more harm than good.
Chemicals have unique application. Read manufacture's directions and warnings.
Brake cleaner is highly flammable, spraying indiscriminately on an running engine is unsafe, catastrophic with an unintended spark and is detrimental on rubber parts nor friendly to electrical components around engine compartment. Use can do more harm than good.
Chemicals have unique application. Read manufacture's directions and warnings.
Drifting
Joined: Feb 2010
Posts: 1,527
Likes: 34
with being a common diagnostic method, but knowledge is power! There are better alternatives, although most are flammable, but not detrimental to paint, rubber or petroleum by products and electrical components. Just like smoking, hazards and warnings are on the label!
To each his own!
Racer
Joined: Oct 2008
Posts: 287
Likes: 1
with being a common diagnostic method, but knowledge is power! There are better alternatives, although most are flammable, but not detrimental to paint, rubber or petroleum by products and electrical components. Just like smoking, hazards and warnings are on the label!
To each his own!
Racer
Joined: Dec 2010
Posts: 418
Likes: 0
From: South Central Kansas
with being a common diagnostic method, but knowledge is power! There are better alternatives, although most are flammable, but not detrimental to paint, rubber or petroleum by products and electrical components. Just like smoking, hazards and warnings are on the label!
To each his own!
Last edited by 1fastbob; Mar 6, 2012 at 07:20 PM.
Drifting
Joined: Feb 2010
Posts: 1,527
Likes: 34
Drifting
Joined: Feb 2010
Posts: 1,527
Likes: 34
I used brake cleaner as an example cause Bill Curlee mentioned it and Bill's advice is pretty solid. I would prefer carb cleaner, but both are flammable and the potential for a small fire exists, but unlikley. Using something that is non-flammable will not get any result. Usually tightening all the connections and checking all the vacuum hoses gets results, but sometimes one has to get down right serious to accomplish the diagnosis. I would caution the OP that if he is not mechanically inclined or does not have a good understanding of how an engine produces vacuum and where to look for vacuum problems that a professional may be required. It is also possible that the OP may not have a vacuum leak. First thing I'd do is disconnect the battery and let the engine relearn the idle. See if that fixes it.
+ for carb cleaner + your logical analysis!I prefer to act basing on facts and not by someone's advice! Here say can be dangerous.
Reminded me prior to 9/11, Navy used to host open house, my past life used to be with DOD, worked in a civilian capacity. Easy access for me to host friends onto Navy vessels during open house. One visit, this particular service ship had a machine shop, not knowing there is a 39 years professional among the audience, the presenter was a senior Navy Chief Machinist Mate, his presentation was on a pump shaft, lathe mounted between centers, he was misleading and full of inaccuracy, to say the least! On the other hand, the lecture might sounded like gospel to the uninformed! We all simply -
and moved on!
Thread Starter
Racer
Joined: Nov 2006
Posts: 448
Likes: 0
From: Dallas, TX
I've never dealt with vacuum problems and haven't troubleshot (sp?) them before, so I'm going to start with cleaning the MAF / TB and checking connections.
Disconnecting the battery clears engine management settings? Given the stored program, I'm a little surprised (but not disagreeing).
Thanks!
Disconnecting the battery clears engine management settings? Given the stored program, I'm a little surprised (but not disagreeing).
Thanks!
Racer
Joined: Mar 2011
Posts: 290
Likes: 0
From: The Colony TX
Had something similar happen about 2 months ago. Had cam/headers and cai installed last summer. The car ran great. Then all of a sudden the car developed a bad idle stumble. When I would push in the clutch and come to a stop, the revs would raise to about 1200 for a few seconds and then fall. Sometimes it would fall on its face and kill the car. Took it to my tuner and he fixed the prob in about 10 min. I was running too rich at idle. I made a post about it and several people said they experienced something similar. Not sure if this is the problem but its worth checking out.
Thread Starter
Racer
Joined: Nov 2006
Posts: 448
Likes: 0
From: Dallas, TX
Quick question -- while I was cleaning the throttle body with carb cleaner, I noticed that the blade doesn't sit all the way closed at the ridge line when disconnected --i.e., the blade can be pushed wide open AND can go back a 1/2" to the ridge where it's fully closed off. Can anyone confirm that's normal?
Thanks!
Thanks!