Hanging engine RPM?
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Hanging engine RPM?
Okay so it's not so much hanging but when I rev the engine up and let off it goes back down steadily but slowly. I know on the older cars they had something on the TB that did this in order to pass emissions to prevent a temporary rich mixture. Is there any way to get rid of this feature?
One of the reasons im concerned and it could be a different problem but sometimes I get a little "blip" in the throttle when I easily take my foot off the gas and most of the time the engine in very jerky after applying light throttle and then letting off even at very low rpm. I also have caught the engine rpm going up a bit briefly when I push in the clutch even when im not giving it any gas. The throttle transition seems to be choppy im not sure if it's due to the engine rpms staying up or something with the throttle by wire system that controls the butterfly valve?
Thanks guys
One of the reasons im concerned and it could be a different problem but sometimes I get a little "blip" in the throttle when I easily take my foot off the gas and most of the time the engine in very jerky after applying light throttle and then letting off even at very low rpm. I also have caught the engine rpm going up a bit briefly when I push in the clutch even when im not giving it any gas. The throttle transition seems to be choppy im not sure if it's due to the engine rpms staying up or something with the throttle by wire system that controls the butterfly valve?
Thanks guys
Safety Car
Joined: Jun 1999
Posts: 3,570
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From: Austin, Singapore, Kuala Lumpur, Houston, Dallas, Hong Kong, Elgin, etc.. Texas
Okay so it's not so much hanging but when I rev the engine up and let off it goes back down steadily but slowly. I know on the older cars they had something on the TB that did this in order to pass emissions to prevent a temporary rich mixture. Is there any way to get rid of this feature?
One of the reasons im concerned and it could be a different problem but sometimes I get a little "blip" in the throttle when I easily take my foot off the gas and most of the time the engine in very jerky after applying light throttle and then letting off even at very low rpm. I also have caught the engine rpm going up a bit briefly when I push in the clutch even when im not giving it any gas. The throttle transition seems to be choppy im not sure if it's due to the engine rpms staying up or something with the throttle by wire system that controls the butterfly valve?
Thanks guys
One of the reasons im concerned and it could be a different problem but sometimes I get a little "blip" in the throttle when I easily take my foot off the gas and most of the time the engine in very jerky after applying light throttle and then letting off even at very low rpm. I also have caught the engine rpm going up a bit briefly when I push in the clutch even when im not giving it any gas. The throttle transition seems to be choppy im not sure if it's due to the engine rpms staying up or something with the throttle by wire system that controls the butterfly valve?
Thanks guys
The jerky or choppy description sound like surging. This also is a tune issue.
If its been modded or tuned, your tuner should be able to fix it.
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Thanks for the responses guys. The car is stock except for K&N air filters however it does feel like a tuning issue because my last car had the same exact problem after I put a full exhaust and intake on it. I guess the best way to describe my issue is it runs as a car would that is cold and has not warmed up to operating temp. I assume that means I might be running a bit lean for whatever reason.
Also is there a way to disable the computer from slowing down the rpm drop between gears? I believe that it is built in for emissions compliance on all newer cars?
Also is there a way to disable the computer from slowing down the rpm drop between gears? I believe that it is built in for emissions compliance on all newer cars?
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From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
If the car is stokc it could have a vacume leak which will hang up the rpm's too. The leak would have to be after the mass air sensor. Check the hoses that lead into the intake manifold and the accordion coupler.
Safety Car
Joined: Jun 1999
Posts: 3,570
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From: Austin, Singapore, Kuala Lumpur, Houston, Dallas, Hong Kong, Elgin, etc.. Texas
Thanks for the responses guys. The car is stock except for K&N air filters however it does feel like a tuning issue because my last car had the same exact problem after I put a full exhaust and intake on it. I guess the best way to describe my issue is it runs as a car would that is cold and has not warmed up to operating temp. I assume that means I might be running a bit lean for whatever reason.
Also is there a way to disable the computer from slowing down the rpm drop between gears? I believe that it is built in for emissions compliance on all newer cars?
Also is there a way to disable the computer from slowing down the rpm drop between gears? I believe that it is built in for emissions compliance on all newer cars?
I don't believe emissions is a factor here. The PCM in conjunction with the NBO2 sensors and cats do a great job in keeping emissions in check.
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Yesterday I gutted the stock cats in preparation for my Borla Stinger catback system. (By the way it was a very quick and easy job!) First thing I notice is when I rev it up and let off the rpms drop a lot quicker now. The engine feels freer both reving up and coming back down and it compliments my vararam intake by giving much stronger, faster and cleaner throttle response! The stock cats appeared to be in excellent like new condition so I don't think they were clogged. Just wanted to update! I am also going to have it tunned after the cam and eventual LG headers & x pipe. I don't know much about the LS2 in comparison to the LS1 but I am going to be looking for a cam very similar to the popular Magic Stick 3/Magic Stick 4 that they make for the LS1. I would buy from LG but they seem to be a tad high on prices.
Last edited by themotoking; Feb 16, 2011 at 07:12 AM.
Tech Contributor
Joined: Dec 2006
Posts: 10,962
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From: Van Buren Arkansas
Wounded Warrior Escort '11
I've noticed this same thing with my '07 but seem to think its related to the factory tuning as mine is stock. When not moving, then the rpm will come down more slowly, but if I'm driving and rev the engine, it'll come down fast.
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Tech Contributor
Joined: Dec 1999
Posts: 32,910
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
I agree with SPIN... Thats a CLASSIC vacuum leak symptom. Especially on a basically STOCK engine.
A couple of things that immediately come to mind are:
The "U" shaped PCV rubber hose that sits on the passengers side of the engine just aft of the TB.
The ducting between the MAF and TB.
Look for any loose clamps of deformed ducting.
After that, them look at other things like a tuning issue but, Its hard to believe a shock engine would have that issue and need a tune to cure it.
BC
A couple of things that immediately come to mind are:
The "U" shaped PCV rubber hose that sits on the passengers side of the engine just aft of the TB.
The ducting between the MAF and TB.
Look for any loose clamps of deformed ducting.
After that, them look at other things like a tuning issue but, Its hard to believe a shock engine would have that issue and need a tune to cure it.
BC
Tech Contributor
Joined: Jul 2002
Posts: 14,950
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From: St. Louis, MO
St. Jude Donor '08
Yesterday I gutted the stock cats in preparation for my Borla Stinger catback system. (By the way it was a very quick and easy job!) First thing I notice is when I rev it up and let off the rpms drop a lot quicker now. The engine feels freer both reving up and coming back down and it compliments my vararam intake by giving much stronger, faster and cleaner throttle response! The stock cats appeared to be in excellent like new condition so I don't think they were clogged. Just wanted to update! I am also going to have it tunned after the cam and eventual LG headers & x pipe. I don't know much about the LS2 in comparison to the LS1 but I am going to be looking for a cam very similar to the popular Magic Stick 3/Magic Stick 4 that they make for the LS1. I would buy from LG but they seem to be a tad high on prices.
By the way, you should know Borla stingers are LOUD LOUD LOUD with headers and cam. I loved them when my car was stock but when I added headers and a cam....it was way too loud to drive in the street every day. Like people look at you at stop lights thinking your exhaust fell off loud. It was embarrassing and I had to replace the stingers. You might want to listen to a cammed car with them before you buy.
A set of factory z06 or npp mufflers are great option for quiet or loud. I have stock mufflers and Qtp cutouts and I love that option too.
Racer
Joined: Mar 2009
Posts: 316
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From: Fort Worth Texas
Give SNL Performance a call for the cam. Their v.X cam is VERY similar in specs to the old MS3 cam.
www.snlperformance.com
www.snlperformance.com
Thread Starter
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Joined: Feb 2011
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Give SNL Performance a call for the cam. Their v.X cam is VERY similar in specs to the old MS3 cam.
www.snlperformance.com
www.snlperformance.com
Thread Starter
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Joined: Feb 2011
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Glad go hear it's running better. I also would have guessed a vacuum leak issue. A stock car shouldn't have a hanging idle.
By the way, you should know Borla stingers are LOUD LOUD LOUD with headers and cam. I loved them when my car was stock but when I added headers and a cam....it was way too loud to drive in the street every day. Like people look at you at stop lights thinking your exhaust fell off loud. It was embarrassing and I had to replace the stingers. You might want to listen to a cammed car with them before you buy.
A set of factory z06 or npp mufflers are great option for quiet or loud. I have stock mufflers and Qtp cutouts and I love that option too.
By the way, you should know Borla stingers are LOUD LOUD LOUD with headers and cam. I loved them when my car was stock but when I added headers and a cam....it was way too loud to drive in the street every day. Like people look at you at stop lights thinking your exhaust fell off loud. It was embarrassing and I had to replace the stingers. You might want to listen to a cammed car with them before you buy.
A set of factory z06 or npp mufflers are great option for quiet or loud. I have stock mufflers and Qtp cutouts and I love that option too.
hmm.. I like it LOUD LOUD but not LOUD LOUD LOUD
If it's too loud maybe I can get an aftermarket butterfly valve system that tones it down when it's before WOT? I watched these clips of a vette with stingers, no cats and headers and it sounded like what I was looking for. It screams up top but idle and around town seems tame enough. http://www.youtube.com/watch?v=mbCQudZFPd8
http://www.youtube.com/watch?v=5aBYrV5ueAQ
Tech Contributor
Joined: Jul 2002
Posts: 14,950
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From: St. Louis, MO
St. Jude Donor '08
hmm.. I like it LOUD LOUD but not LOUD LOUD LOUD If it's too loud maybe I can get an aftermarket butterfly valve system that tones it down when it's before WOT? I watched these clips of a vette with stingers, no cats and headers and it sounded like what I was looking for. It screams up top but idle and around town seems tame enough.
http://www.youtube.com/watch?v=mbCQudZFPd8
http://www.youtube.com/watch?v=5aBYrV5ueAQ
If it's too loud maybe I can get an aftermarket butterfly valve system that tones it down when it's before WOT? I watched these clips of a vette with stingers, no cats and headers and it sounded like what I was looking for. It screams up top but idle and around town seems tame enough. http://www.youtube.com/watch?v=mbCQudZFPd8
http://www.youtube.com/watch?v=5aBYrV5ueAQ
It really limits the car...the only appropriate place for a car that loud is the racetrack or a car show. Daily driving is a drag.
And the drone on the stingers is deafening at 1800 rpm... highway speeds with headers/cam.
I strongly suggest you go for a ride in a car with any loud exhaust before you spend your money. Videos don't do it justice. Or just go the cheap option with the Z06 mufflers, that is a no brainer. Loud or quiet, your choice.
