Post by Fire67 on Aug 11, 2006 14:06:53 GMT -5
Aftermarket Throttle Body/ TPS/ IAC adjustment:
First off, contrary to what some may believe, to adjust any of these properly you actually need to adjust all three. This is because of how they all work together both mechanically and electronically. The TPS sensor is a potentiometer that sends a position signal to the PCM by increasing voltage as the Throttle blade open. This affects fuel and ignition maps in the PCM’s programming along with information received from other sensors such as the MAF, O2’s, etc. The PCM also relies on the TPS and other information to control the IAC motor and the idle.
One exception to this is with a Factory throttle body on a stock motor. By stock I mean stock cam, stock heads, stock displacement. In such a situation the procedure should not even be needed at all.
When you go beyond “stock” with your mill, you have increased the motors demand for air, especially with larger than stock engine displacement. Unfortunately, there are so many engine combinations out there that aftermarket companies cannot size the IAC bleed hole in their TB’s to work for every app. They usually merely copy the diameter of the stock hole.
I will attempt to explain the necessary steps to adjusting these components in conjunction with each other, so that they work together properly and allow the PCM to control your motor as it should. As far as these components are concerned anyway.
The key will be to ensure enough bleed air so that a proper idle, TPS voltage range, and IAC counts are obtained.
1) Back of Throttle Blade adjustment (set) screw until it no longer makes contact with the throttle linkage arm. Then bring it back out until it JUST contacts the linkage again, at this point turn the screw another ¼ to ½ turn in the same direction. Your blades are no positioned correctly
2) Remove the TPS sensor and elongate the mounting holes slightly in both directions to allow + or – adjustments. Re-install and set the output voltage to read .69-.71 with the TB in the closed (idle) position. The ignition switch must be in the run position to do this. Then check the voltage output with the TB in the WOT position. (Engine not running of course ) This should be approximately 4.5v. If too low, adjust the TPS idle setting up slightly until you get at least 4.5v at the WOT postion.
3) At this point check your IAC counts via a scanner or scan software. The ideal counts to see with the engine idling are mid to upper 30’s. If you see them in the 140-160 range, the IAC pintle is adjusted almost to its max. This will not leave enough room for the PCM to compensate for all the possible engine load conditions like A/C. Basically your motor is demanding more air at idle than your PCM/ IAC system is capable of providing it. If your counts are anywhere above mid to upper 30’s, you need to adjust them by changing the size of the bleed hole.
4) If the counts are high increase hole size in the smallest increments possible to dial it in to the 34-39 range. Its always better to start with too small of a hole than to start with too large of one. Of course, if you over do it and zero out your IAC counts at idle, you will notice the PCM has a hard time getting the idle to fall to its target as the motor is getting too much air. In this case, you would need to fill the hole with Moroso A+B epoxy or similar and re-drill to a smaller size.
In summary, you need to set the TPS voltage, set the expected idle in the PCM and check the IAC counts. If the count is high, enlarge the hole. If they’re low reduce the diameter of the hole.
You will probably have to remove the TB several times and experiment with the hole size untill you get it right. Definitely can be a pain, but it’s the best way to ensure that you will have everything functioning properly. Go slow, take small steps, and enjoy your newfound idle quality again.
This worked on my motor, which had difficulty idling to begin with, let alone if I tried to turn on the A/C. Because everything was so far off with my setup, I also had problems with a hanging idle when I would clutch or neutral out to slow start slowing down. Dialing in my TB blades, TPS, bleed hole size made it drive like it should again.
First off, contrary to what some may believe, to adjust any of these properly you actually need to adjust all three. This is because of how they all work together both mechanically and electronically. The TPS sensor is a potentiometer that sends a position signal to the PCM by increasing voltage as the Throttle blade open. This affects fuel and ignition maps in the PCM’s programming along with information received from other sensors such as the MAF, O2’s, etc. The PCM also relies on the TPS and other information to control the IAC motor and the idle.
One exception to this is with a Factory throttle body on a stock motor. By stock I mean stock cam, stock heads, stock displacement. In such a situation the procedure should not even be needed at all.
When you go beyond “stock” with your mill, you have increased the motors demand for air, especially with larger than stock engine displacement. Unfortunately, there are so many engine combinations out there that aftermarket companies cannot size the IAC bleed hole in their TB’s to work for every app. They usually merely copy the diameter of the stock hole.
I will attempt to explain the necessary steps to adjusting these components in conjunction with each other, so that they work together properly and allow the PCM to control your motor as it should. As far as these components are concerned anyway.
The key will be to ensure enough bleed air so that a proper idle, TPS voltage range, and IAC counts are obtained.1) Back of Throttle Blade adjustment (set) screw until it no longer makes contact with the throttle linkage arm. Then bring it back out until it JUST contacts the linkage again, at this point turn the screw another ¼ to ½ turn in the same direction. Your blades are no positioned correctly
2) Remove the TPS sensor and elongate the mounting holes slightly in both directions to allow + or – adjustments. Re-install and set the output voltage to read .69-.71 with the TB in the closed (idle) position. The ignition switch must be in the run position to do this. Then check the voltage output with the TB in the WOT position. (Engine not running of course
) This should be approximately 4.5v. If too low, adjust the TPS idle setting up slightly until you get at least 4.5v at the WOT postion.3) At this point check your IAC counts via a scanner or scan software. The ideal counts to see with the engine idling are mid to upper 30’s. If you see them in the 140-160 range, the IAC pintle is adjusted almost to its max. This will not leave enough room for the PCM to compensate for all the possible engine load conditions like A/C. Basically your motor is demanding more air at idle than your PCM/ IAC system is capable of providing it. If your counts are anywhere above mid to upper 30’s, you need to adjust them by changing the size of the bleed hole.
4) If the counts are high increase hole size in the smallest increments possible to dial it in to the 34-39 range. Its always better to start with too small of a hole than to start with too large of one. Of course, if you over do it and zero out your IAC counts at idle, you will notice the PCM has a hard time getting the idle to fall to its target as the motor is getting too much air. In this case, you would need to fill the hole with Moroso A+B epoxy or similar and re-drill to a smaller size.
In summary, you need to set the TPS voltage, set the expected idle in the PCM and check the IAC counts. If the count is high, enlarge the hole. If they’re low reduce the diameter of the hole.
You will probably have to remove the TB several times and experiment with the hole size untill you get it right. Definitely can be a pain, but it’s the best way to ensure that you will have everything functioning properly. Go slow, take small steps, and enjoy your newfound idle quality again.
This worked on my motor, which had difficulty idling to begin with, let alone if I tried to turn on the A/C. Because everything was so far off with my setup, I also had problems with a hanging idle when I would clutch or neutral out to slow start slowing down. Dialing in my TB blades, TPS, bleed hole size made it drive like it should again.
