Setting idle screw on TB
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BEATAV8
The Engine Whisperer
- Joined
- Feb 14, 2002
- Messages
- 5,747
the goal is 10-15 IAC counts warm idle in park. If you have more than that you need to open the throttle blade. If you have less you need to close the throttle blade.
During all this adjustment you also need to keep tps close to .42v
So you may need to go back and forth between screw adjustment and tps adjustment.
Tps voltage being close to .42 v is what tells the computer it’s time to idle and use / control the IAC. If the voltage gets too far away then the computer will think you are driving and it’s not time to idle.
During all this adjustment you also need to keep tps close to .42v
So you may need to go back and forth between screw adjustment and tps adjustment.
Tps voltage being close to .42 v is what tells the computer it’s time to idle and use / control the IAC. If the voltage gets too far away then the computer will think you are driving and it’s not time to idle.
- Joined
- May 27, 2001
- Messages
- 9,483
The official way to set it is to run the IAC closed and unplug it. Get the idle to within like 100 RPM of whatever the chip is asking for and then reconnect the IAC after making sure your TPS isnt out of range.
- Joined
- May 27, 2001
- Messages
- 9,483
Yea, the manual.
You have to jump a couple of ports in the ALDL connector. I forget which two it is. Keep the jumper in for like a minute and then unplug the IAC.
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- Apr 26, 2018
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I use this procedure although I have an 85 harness, but I think it's the same for both.........
Loop status should not matter to get the minimum air rate correct. You do need to get the engine full warmed up. To set minimum air rate:
1. Warm the engine to full operating temps
2. Turn engine off and then turn the key back to ON
3. With the IAC connected, jumper pins A and B at the ALDL.
4. Wait 30 seconds and unplug the IAC
5. Remove the jumper at the ALDL
6. Start the engine
7. Adjust engine RPM to 500-550 in Drive using the throttle stop screw on the throttle body.
8. Shut the engine off and plug the IAC back in.
9. Restart the engine
10. Set TPS to .40-.44 volt or whatever your chip manufacturer specifies
At full operating temps, the IAC counts on a scanmaster or scan tool should be somewhere in the 20-40 count range at idle. The IAC counts go up as you open the throttle (throttle follower function)
If you have a vacuum leak, you may not be able to obtain a low enough idle speed during the above procedure. Air is entering the intake manifold and not going through the throttle body.
-----------------------------------------------------------
IAC Reset Procedure with a Scan Tool - alternatively, a digital voltmeter
Turbobuick.com thread by - Ken Mosher
Procedure
The ECM controls idle rpm with the IAC (idle air control) valve. The idle rpm is programmed into the PROM. To increase idle rpm the ECM moves the IAC valve out allowing more air to pass by the throttle plate. To decrease rpm it moves the IAC valve in to reduce air past the throttle plate. A scan tool will read the ECM commands to the IAC valve in counts. Higher the counts the more the air is being allowed to pass the throttle plate (higher idle). Lower the counts the less the air is being allowed to pass the throttle plate (lower idle).
Warm the engine to normal operating temperature. This is important ... the car needs to be in closed loop.
Connect scan tool. Verify it's in closed loop.
Put the car in park and wait a couple seconds for it to settle into a regular idle.
Look at the IAC counts (# and not % in TurboLink™)
If the IAC counts are between 10-40, then it's pretty close. Otherwise, do the following adjustment procedure, with a target number of around 20-25 counts.
The Minimum Air adjustment screw is on the driver’s side of the throttle body on the throttle linkage arm (often times misunderstood as the "idle adjustment screw". Pull off the gray rubber cable protecting the screw head.
Turn the screw in VERY small amounts (1/4 turn or so) to adjust the Minimum Air setting. Turning it counter clockwise closes the throttle blade and will normally raise the IAC counts. Turning it clockwise opens the throttle blade and will normally lower IAC counts.
Carefully monitor the IAC counts while making small adjustments to the Minimum Air setting screw. Be sure to allow the car to "settle" a bit after each adjustment a couple of seconds.
Once you have IAC counts adjusted to within your target range, adjust the TPS as described HERE.
Adjusting the TPS
Turbobuick.com thread by - Ken Mosher
Objective
To adjust the Throttle Position Sensor to recommended settings of between 0.40-0.46 volts at idle and between 4.5 and 4.8 volts at Wide Open Throttle (WOT). This procedure should be performed after the minimum idle air settings are already made (via the IAC reset procedure).
Equipment Needed
The following tools are needed:
Flat bladed screwdriver
Scan tool (alternatively, a digital voltmeter)
Procedure
Hook up your scan tool where you can see the readings clearly from under the hood (alternatively, back probe the TPS blue wire with the positive lead of the meter and ground the meter's negative lead to the chassis or battery)
Turn the key ON and leave the engine OFF
Loosen the two screws on the side of the sensor (passenger side of the throttle body) enough to allow you to move the sensor in the "moon shaped" grooves.
Grab the "nose" of the sensor (where the wires plug in) and pull the sensor as far forward as possible and snug the screws enough that it holds the sensor in place (but can still be moved if nudged)
Check the idle reading and tap the nose of the sensor up or down until you get an idle reading of between 0.40 and 0.46 volts. Anything above about 0.5 volts will not be seen as "idle" by the ECM and can cause drivability problems.
Snug the screws down tight enough that the sensor doesn't move and have someone floor the throttle (make sure that the floor mat is out of the car...)
Check the reading and adjust until the sensor reads between 4.55 volts and 4.85 volts. The intent is to make sure that the reading is high enough that the ECM reads full WOT. The actual number doesn't really matter as long as it is with the range.
Recheck the idle reading to make sure that it hasn't changed. This can be a bit of a balancing act and require some very small adjustments and several iterations before both the high and low settings are where you want them to be.
Note: Occasionally a TPS will need the moon shaped grooves honed out a bit with a rat tail file to get enough adjustment, but normally the trick of moving the sensor as far forward as possible gives enough adjustment. Also, be very careful around the little roll pin that rests on the throttle lever, since it can bend or break.
Loop status should not matter to get the minimum air rate correct. You do need to get the engine full warmed up. To set minimum air rate:
1. Warm the engine to full operating temps
2. Turn engine off and then turn the key back to ON
3. With the IAC connected, jumper pins A and B at the ALDL.
4. Wait 30 seconds and unplug the IAC
5. Remove the jumper at the ALDL
6. Start the engine
7. Adjust engine RPM to 500-550 in Drive using the throttle stop screw on the throttle body.
8. Shut the engine off and plug the IAC back in.
9. Restart the engine
10. Set TPS to .40-.44 volt or whatever your chip manufacturer specifies
At full operating temps, the IAC counts on a scanmaster or scan tool should be somewhere in the 20-40 count range at idle. The IAC counts go up as you open the throttle (throttle follower function)
If you have a vacuum leak, you may not be able to obtain a low enough idle speed during the above procedure. Air is entering the intake manifold and not going through the throttle body.
-----------------------------------------------------------
IAC Reset Procedure with a Scan Tool - alternatively, a digital voltmeter
Turbobuick.com thread by - Ken Mosher
Procedure
The ECM controls idle rpm with the IAC (idle air control) valve. The idle rpm is programmed into the PROM. To increase idle rpm the ECM moves the IAC valve out allowing more air to pass by the throttle plate. To decrease rpm it moves the IAC valve in to reduce air past the throttle plate. A scan tool will read the ECM commands to the IAC valve in counts. Higher the counts the more the air is being allowed to pass the throttle plate (higher idle). Lower the counts the less the air is being allowed to pass the throttle plate (lower idle).
Warm the engine to normal operating temperature. This is important ... the car needs to be in closed loop.
Connect scan tool. Verify it's in closed loop.
Put the car in park and wait a couple seconds for it to settle into a regular idle.
Look at the IAC counts (# and not % in TurboLink™)
If the IAC counts are between 10-40, then it's pretty close. Otherwise, do the following adjustment procedure, with a target number of around 20-25 counts.
The Minimum Air adjustment screw is on the driver’s side of the throttle body on the throttle linkage arm (often times misunderstood as the "idle adjustment screw". Pull off the gray rubber cable protecting the screw head.
Turn the screw in VERY small amounts (1/4 turn or so) to adjust the Minimum Air setting. Turning it counter clockwise closes the throttle blade and will normally raise the IAC counts. Turning it clockwise opens the throttle blade and will normally lower IAC counts.
Carefully monitor the IAC counts while making small adjustments to the Minimum Air setting screw. Be sure to allow the car to "settle" a bit after each adjustment a couple of seconds.
Once you have IAC counts adjusted to within your target range, adjust the TPS as described HERE.
Adjusting the TPS
Turbobuick.com thread by - Ken Mosher
Objective
To adjust the Throttle Position Sensor to recommended settings of between 0.40-0.46 volts at idle and between 4.5 and 4.8 volts at Wide Open Throttle (WOT). This procedure should be performed after the minimum idle air settings are already made (via the IAC reset procedure).
Equipment Needed
The following tools are needed:
Flat bladed screwdriver
Scan tool (alternatively, a digital voltmeter)
Procedure
Hook up your scan tool where you can see the readings clearly from under the hood (alternatively, back probe the TPS blue wire with the positive lead of the meter and ground the meter's negative lead to the chassis or battery)
Turn the key ON and leave the engine OFF
Loosen the two screws on the side of the sensor (passenger side of the throttle body) enough to allow you to move the sensor in the "moon shaped" grooves.
Grab the "nose" of the sensor (where the wires plug in) and pull the sensor as far forward as possible and snug the screws enough that it holds the sensor in place (but can still be moved if nudged)
Check the idle reading and tap the nose of the sensor up or down until you get an idle reading of between 0.40 and 0.46 volts. Anything above about 0.5 volts will not be seen as "idle" by the ECM and can cause drivability problems.
Snug the screws down tight enough that the sensor doesn't move and have someone floor the throttle (make sure that the floor mat is out of the car...)
Check the reading and adjust until the sensor reads between 4.55 volts and 4.85 volts. The intent is to make sure that the reading is high enough that the ECM reads full WOT. The actual number doesn't really matter as long as it is with the range.
Recheck the idle reading to make sure that it hasn't changed. This can be a bit of a balancing act and require some very small adjustments and several iterations before both the high and low settings are where you want them to be.
Note: Occasionally a TPS will need the moon shaped grooves honed out a bit with a rat tail file to get enough adjustment, but normally the trick of moving the sensor as far forward as possible gives enough adjustment. Also, be very careful around the little roll pin that rests on the throttle lever, since it can bend or break.
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