ported throttle body problem
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From: Bellevue, WA.
ported throttle body problem I got this ported throttle body with an ls6 intake manifold, and i absolutely have no idea what is wrong with it! it idles at 1500rpm when car starts to move, if i make a full stop it goes back to 650-700 rpm. If im downhill and let car go it goes up to 1500rpm... Is this a common problem? Is anyone experienced such thing before?
Thanks in advance
Thanks in advance
Check all the wires on the TB - the idle is controlled by that little step motor there - it's held in place by two torx bolts if I remember right.
Also make sure the cable isn't getting stuck anywhere. I installed my Shaner S3 a while back and the cable was out of place but in my case it revved up to 4k
That's all I can tell from my TB install experience, I'm sure Ellis and others will have more advices for ya!
Also make sure the cable isn't getting stuck anywhere. I installed my Shaner S3 a while back and the cable was out of place but in my case it revved up to 4k
That's all I can tell from my TB install experience, I'm sure Ellis and others will have more advices for ya!
Would have to see the throttle body. I ported my TB myself with a dremel tool and have 0 problems. There are a few things that could cause it...if the porting is overdone it can cause bad idle. Also I didn't do any epoxy..if the hole where most do the epoxy inside the TB is clogged it can make the car idle bad too...
How big is the hole in the TB blade? I think stock is around 1/8". Most likely this came from a car with a cam, and they enlarged the hole to make it idle....which causes this "cruise control" issue.
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hmmm thanks a lot guys, i bought it from a friends friend of mine, im gonna ask how big the hole is or I can just go ahead and measure it 
But yeah that makes sense maybe it is a big hole...
But yeah that makes sense maybe it is a big hole... Got some drill bits? Stick them in until you find out how big it is. When I get home I will take measurements & tell you how big the stock one is, and how big mine is (been enlarged for a cam)
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When cruising or when coming to a stop, the ECU "parks" the IAC without thinking enough about it at a static location. If the throttle set screw is set wrong, then that will be off, and the coasting idle can be too high, too low, etc.
In order to set the throttle set screw at the best location, unplug the IAC (Idle air control), start the car, and then turn the idle set screw (tough to do when the car is on... you may have to turn it off, turn the screw, turn the car back on, see where it idles, etc) until the car idles about 50 rpm less than your normal desired idle.
When you replug in the IAC, the car now will have the TPS (throttle position sensor) set wrong. To fix that, unplug the TPS sensor (next to the IAC on the TB), and then turn the car to "on" (you dont have to start it) for about 10 seconds. Then turn it off and go plug the TPS back in. Now restart the car.
The car should now "park" the IAC pintle in a more reasonable place when you are coasting or coming to a stop. This all is a pretty fragile setting too, so it may take some time to get the throttle set screw juuuuuuust right for your tastes. Unfortunately you have to perform the TPS relearn that I just described each time you move the throttle set screw much, otherwise the idle can behave really strangely.
Chris
In order to set the throttle set screw at the best location, unplug the IAC (Idle air control), start the car, and then turn the idle set screw (tough to do when the car is on... you may have to turn it off, turn the screw, turn the car back on, see where it idles, etc) until the car idles about 50 rpm less than your normal desired idle.
When you replug in the IAC, the car now will have the TPS (throttle position sensor) set wrong. To fix that, unplug the TPS sensor (next to the IAC on the TB), and then turn the car to "on" (you dont have to start it) for about 10 seconds. Then turn it off and go plug the TPS back in. Now restart the car.
The car should now "park" the IAC pintle in a more reasonable place when you are coasting or coming to a stop. This all is a pretty fragile setting too, so it may take some time to get the throttle set screw juuuuuuust right for your tastes. Unfortunately you have to perform the TPS relearn that I just described each time you move the throttle set screw much, otherwise the idle can behave really strangely.
Chris
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Verdad Gallardo Also, remember that there is a little idle learning going on... so oftentimes the car will learn for itself some of the finer details. If its off aways or you've driven it alot adn it hasnt gotten better, the procedure above will be necessary.
I dont remember offhand how big the hole in the TB was. Theres some JB-weld in there where I brought the size back down to what I *thought* was stock or close to it. Using this TB-set-screw method can counteract (to a point) any hole size imperfections. I returned the hole in this TB towards stock because I learned to use the set-screw (as above).
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From: Fredericksburg, VA
Your problem is most likely being caused by the new TB having an increased flow area at 0 throttle, due to a larger bypass hole and/or where the set screw is positioned. These modifications throw a monkey wrench into the IAC Position vs. Effective Area table, which causes the "cruise effect" and hanging idle. Basically, this table specifies a cross sectional area of airflow (the effective area) for a given position of the IAC motor (known as IAC steps). When the TB bypass hole is widened, or the set screw is adjusted, the effective area for all IAC steps is increased, necessitating that the IAC Position vs. Effective Area table be modified to reflect the increased airflow.
This concept is easy to see in action if you log Desired Idle Airflow and actual MAF Airflow in a program like HPTuner. With a modified TB and a stock table, you might have a Desired Idle Airflow of 1.2 lb/min, but your actual MAF Airflow would be higher, at say 1.4 lb/min. This is because the IAC motor sets itself for the desired amount of airflow using the values in the IAC Position vs. Effective Area table. This extra airflow is what causes the cruise effect and hanging idle.
To correct the table, you need to shift the values (which are the IAC steps) to the right, until your MAF Airflow matches you Desired Idle Airflow. Basically just cutting and pasting the values a couple cells to the right, logging each time, until your desired and actual airflow values match up.
This concept is easy to see in action if you log Desired Idle Airflow and actual MAF Airflow in a program like HPTuner. With a modified TB and a stock table, you might have a Desired Idle Airflow of 1.2 lb/min, but your actual MAF Airflow would be higher, at say 1.4 lb/min. This is because the IAC motor sets itself for the desired amount of airflow using the values in the IAC Position vs. Effective Area table. This extra airflow is what causes the cruise effect and hanging idle.
To correct the table, you need to shift the values (which are the IAC steps) to the right, until your MAF Airflow matches you Desired Idle Airflow. Basically just cutting and pasting the values a couple cells to the right, logging each time, until your desired and actual airflow values match up.
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Originally Posted by Silverhawk_02TA
Your problem is most likely being caused by the new TB having an increased flow area at 0 throttle, due to a larger bypass hole and/or where the set screw is positioned. These modifications throw a monkey wrench into the IAC Position vs. Effective Area table, which causes the "cruise effect" and hanging idle. Basically, this table specifies a cross sectional area of airflow (the effective area) for a given position of the IAC motor (known as IAC steps). When the TB bypass hole is widened, or the set screw is adjusted, the effective area for all IAC steps is increased, necessitating that the IAC Position vs. Effective Area table be modified to reflect the increased airflow.
This concept is easy to see in action if you log Desired Idle Airflow and actual MAF Airflow in a program like HPTuner. With a modified TB and a stock table, you might have a Desired Idle Airflow of 1.2 lb/min, but your actual MAF Airflow would be higher, at say 1.4 lb/min. This is because the IAC motor sets itself for the desired amount of airflow using the values in the IAC Position vs. Effective Area table. This extra airflow is what causes the cruise effect and hanging idle.
To correct the table, you need to shift the values (which are the IAC steps) to the right, until your MAF Airflow matches you Desired Idle Airflow. Basically just cutting and pasting the values a couple cells to the right, logging each time, until your desired and actual airflow values match up.
This concept is easy to see in action if you log Desired Idle Airflow and actual MAF Airflow in a program like HPTuner. With a modified TB and a stock table, you might have a Desired Idle Airflow of 1.2 lb/min, but your actual MAF Airflow would be higher, at say 1.4 lb/min. This is because the IAC motor sets itself for the desired amount of airflow using the values in the IAC Position vs. Effective Area table. This extra airflow is what causes the cruise effect and hanging idle.
To correct the table, you need to shift the values (which are the IAC steps) to the right, until your MAF Airflow matches you Desired Idle Airflow. Basically just cutting and pasting the values a couple cells to the right, logging each time, until your desired and actual airflow values match up.
Btw I went back to stock TB with ls6 intake it didn't fix the problem [just wanted to let you know]
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From: Fredericksburg, VA
Originally Posted by yekta
I have the HP Tuner, I'll try that thanks a lot for the post!!!
Btw I went back to stock TB with ls6 intake it didn't fix the problem [just wanted to let you know]
Btw I went back to stock TB with ls6 intake it didn't fix the problem [just wanted to let you know]
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Originally Posted by Silverhawk_02TA
If that's the case then you probably have other things going on as well. Start checking for vacuum leaks, since it happened after you installed the LS6 intake, and make sure your RAF table is dialed in correctly.
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I went thought this as well. As it turned out I had routed the cable in front of the tower brace not behind it. I found it hard to believe that routing made a difference but it did. Good luck.
A good way to check for vacuum leaks is to hook up HP Tuner (or equiv) start the engine & look at your ltft's. If they are high, like in the +15 to 25 range, then you are getting air into the system after the MAF (i.e. a leak) that the PCM is dumping fuel in to compensate for.