Idle problem after 52mm ported TB install
Idle problem after 52mm ported TB install I just installed a ported 52mm throttle body and now I'm having some idle issues. What is happening is when you hit the gas or open the blades by hand, they will get stuck and don't close all the way. They won't close enough to rest on the idle set screw.
It only does it when the car is running. With the car off, the blades close all the way easily. They open nice and easy with little effort too. Now with the car running, they are much harder to tip open by hand and won't close unless forced.
What could be causing this? I don't think it's the blades physically catching on the inside of the TB because the problem doesn't happen with the car off.
It only does it when the car is running. With the car off, the blades close all the way easily. They open nice and easy with little effort too. Now with the car running, they are much harder to tip open by hand and won't close unless forced.
What could be causing this? I don't think it's the blades physically catching on the inside of the TB because the problem doesn't happen with the car off.
On The Tree
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My first thought was that the idle air controller or throttle position sensor is interfering with how the blades close, but I don't remember if either one of those systems actually physically interacts with the butterflies.
Now you said when its off, it closes easily? What about when the car is hot and cold as well as on and off? If the engine were hot, the throttle body housing would expand slightly from being warm and if the butterfly tolerances were a little on the big side it would cause them to bind when warm. But when you shut the motor off warm and it closes easily, that is strange.
First thing I'd do is take off the throttle body, take off the TPS and IAC then clean the whole thing real well with carb cleaner (wear gloves and do it outside, that stuff is nasty). Then maybe use a little penetrating oil on the coiled spring and shaft where it attaches to the butterfly. Don't go too hog wild with the oil, you don't want it getting sucked into the motor. Spray some on the contact points, let it soak, and buff the excess off.
If that doesn't work and no one else comes up with any better ideas, return it.
Now you said when its off, it closes easily? What about when the car is hot and cold as well as on and off? If the engine were hot, the throttle body housing would expand slightly from being warm and if the butterfly tolerances were a little on the big side it would cause them to bind when warm. But when you shut the motor off warm and it closes easily, that is strange.
First thing I'd do is take off the throttle body, take off the TPS and IAC then clean the whole thing real well with carb cleaner (wear gloves and do it outside, that stuff is nasty). Then maybe use a little penetrating oil on the coiled spring and shaft where it attaches to the butterfly. Don't go too hog wild with the oil, you don't want it getting sucked into the motor. Spray some on the contact points, let it soak, and buff the excess off.
If that doesn't work and no one else comes up with any better ideas, return it.
Yeah it's a ported stocker, 52mm with aluminum blades installed. When the car is off, not running, hot or cold, the blades close easily by themselves.
When the car is running, hot or cold, they will not fully close once you have opened them by hitting the gas unless you force them closed with your finger.
I sprayed PB Blaster on the coiled spring and it didn't help. I don't understand why it is only doing it with the car running. The blades are also much harder to tip open while the car is running but this could just be because of the incoming air adding resistance.
I'm stumped... it's not a HUGE problem, but it's causing the idle to get stuck at 800-900 instead of the 650 it usually idles at.
The car is a 96 Roadmaster with the LT1, all stock except for this TB, airfoil, cold air intake, mechanical fan delete, 1LE elbow, and a B&M shift improver. Just little bolt ons.
When the car is running, hot or cold, they will not fully close once you have opened them by hitting the gas unless you force them closed with your finger.
I sprayed PB Blaster on the coiled spring and it didn't help. I don't understand why it is only doing it with the car running. The blades are also much harder to tip open while the car is running but this could just be because of the incoming air adding resistance.
I'm stumped... it's not a HUGE problem, but it's causing the idle to get stuck at 800-900 instead of the 650 it usually idles at.
The car is a 96 Roadmaster with the LT1, all stock except for this TB, airfoil, cold air intake, mechanical fan delete, 1LE elbow, and a B&M shift improver. Just little bolt ons.
From BBK web Site on this same isue. I had this problem and did what they said...adjusted TPS voltage and problem solved.
Q. Why is my Throttle body sticking closed near Idle?
This condition is sometimes known as "vacuum lock." There is an extreme amount of vacuum pressure on the backside of the plate, and a large pressure difference from that of the front side. When this happens, the throttle blade tends to want to stay in the closed position, due in large part to the intense vacuum pressure created by the engine. Simply using the Idle set screw (gold colored screw which the linkage rests against) to prop open the blade a tiny bit more will usually solve the problem by allowing more air to pass through the opening, thus better equalizing the pressure and alleviating the "lock." Remember to do small increments at a time, maybe ¼- to ½-turn each attempt.
You can adjust the idle set screew on these cars since there is a level of air comming through the IAC valve. The PCM will adjust this IAC valve more open or closed to reach the desiered idle speed set in the PCM. As long as the TPS voltage is with in rage of like .55 to .70 volts at idle and the iac counts are with in range it will idle good.
Q. Why is my Throttle body sticking closed near Idle?
This condition is sometimes known as "vacuum lock." There is an extreme amount of vacuum pressure on the backside of the plate, and a large pressure difference from that of the front side. When this happens, the throttle blade tends to want to stay in the closed position, due in large part to the intense vacuum pressure created by the engine. Simply using the Idle set screw (gold colored screw which the linkage rests against) to prop open the blade a tiny bit more will usually solve the problem by allowing more air to pass through the opening, thus better equalizing the pressure and alleviating the "lock." Remember to do small increments at a time, maybe ¼- to ½-turn each attempt.
You can adjust the idle set screew on these cars since there is a level of air comming through the IAC valve. The PCM will adjust this IAC valve more open or closed to reach the desiered idle speed set in the PCM. As long as the TPS voltage is with in rage of like .55 to .70 volts at idle and the iac counts are with in range it will idle good.
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TECH Veteran
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OP
Assumeing there is no defect in the stock rebore you really need a scan tool to read IAC counts. I suspect yours are high and the IAC valve can no longer adjust the blades any further.
IAC counts with engine warm at idle want to be 30-35 (32). Typically idle issues with larger TB's are to low and car stalls so adjustments like drill mod are done. Yours is the opposite.
If you pressed in the prindle of the IAC valve when swaping over to the 52 you could have damage it making it the issue.
With your mods the 52 won't really give you any noticeable performance advantage. You also need to have your PCM recalibrated to increase line pressure to tranny or premature failure will happen
Assumeing there is no defect in the stock rebore you really need a scan tool to read IAC counts. I suspect yours are high and the IAC valve can no longer adjust the blades any further.
IAC counts with engine warm at idle want to be 30-35 (32). Typically idle issues with larger TB's are to low and car stalls so adjustments like drill mod are done. Yours is the opposite.
If you pressed in the prindle of the IAC valve when swaping over to the 52 you could have damage it making it the issue.
With your mods the 52 won't really give you any noticeable performance advantage. You also need to have your PCM recalibrated to increase line pressure to tranny or premature failure will happen
TECH Veteran
Joined: Apr 2008
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swapping a stock rebore 52 on a basically stock motor should be a plug & play deal. If you put the 48 back on using the same IAC & TPS and it runs fine (idle) than 'something" is not right with the 52.
It is best not to play around with throttle stop screw as that effects TPS volts. You can slot the holes in the TPS to correct but your issue is opposite what normally is a low idle issue on larger TB swaps, especially on head/cam motors.
you can read TPS volts with a volt meter. .67vdc closed and 4.5 vdc full open. A scan tool is needed to read IAC counts.
Assumeing there is nothing physically wrong with the 52 and the throtle cable is connected right you will need to read that data to determine wtf may be going on with IAC counts.
and I assume you confirmed there are no vacumn leaks causing the high idle
It is best not to play around with throttle stop screw as that effects TPS volts. You can slot the holes in the TPS to correct but your issue is opposite what normally is a low idle issue on larger TB swaps, especially on head/cam motors.
you can read TPS volts with a volt meter. .67vdc closed and 4.5 vdc full open. A scan tool is needed to read IAC counts.
Assumeing there is nothing physically wrong with the 52 and the throtle cable is connected right you will need to read that data to determine wtf may be going on with IAC counts.
and I assume you confirmed there are no vacumn leaks causing the high idle
Yeah dude the TB is PHYSICALLY STICKING OPEN and the blades are not catching, there is no vacuum leak. Something is keeping it from closing all the way and resting on the idle set screw. It seems like a pressure issue like jaycenk suggested because it will close if you push it.
The system is designed to be adjustable. There is a certain amount of unmetered air accounted for in the tune stock or not. The TPS and other inputs into the PCM help the PCM find the correct or desired idle speed. if it is unattainable by the PCM it is usually due to mechanical problems like TB blades open to far, faulty inputs, unmetered air, leaking fuel injector or too high or low of fuel pressure. As long as the everything is with in a range through all of the system there wont be a problem. I do agree that if you have to change the TB blade position that you NEED to see what it does to the IAC counts and tps voltage as I said. If that’s with in range with A/C off and on at cold and at temp you are fine. The PCM wont care how far they blades are open to a point due to the IAC valve it's self. Its whole purpose is to control the idle. When the engine gets hot the clearances change on the TB bore and blades. While its not a lot it is controllable through the IAC valve and the PCM inputs in closed loop. This is the way it was explained to me from BBK and backed up more or less by my GM mechanic. IF I am wrong please tell me and I shut my mouth but as far as I understand it once you have changed from a stock TB the varibles change due to different clearances ect.
Last edited by jaycenk; Oct 21, 2011 at 07:42 PM.
