hoser
SILVER Star
Adjusting your AHC sensors are fairly easy 
banana: job). You'll need to furnish/fabricate a simple bracket extension which I'll cover in step 5. You'll also need one can of AHC fluid from Toyota $22/can. (part # 08886-01805). I have heard the exact fluid costs more if bought from Lexus.
1. Take measurements of your ride height at each corner of the vehicle. I recommend measuring from the fender lip to the bottom wheel lip.
2. Turn off ignition. Locate the Height Control Sensor as seen in the diagram. Note the position on the adjustable top mount. You are going to want to slide it up as far as possible in the next step. For better access to the height control sensor, you can turn the wheels full left/right.
3. I found it easiest to just remove the top nut of the heim joint (10mm) and adjust the rod so that it is as short as possible. This will give you about 2" of lift in the front. If you want 2.5", you'll have to shorten the heim joint (I used a cut-off wheel) and then used the existing stop-nuts to "smooth out the thread" and actually remove the stop nuts completely. Be careful because one side is a reverse thread. Not many people I know have a reverse cut tap/die set.
Once done, reinstall the heim joint and adjust it so that the Height Control Sensor lever is as high as possible. Remount the wheels. You can readust the sensor through the wheel-well later. Make sure ALL adjustments are done while the vehicle is OFF for safety reasons!
4. After the front sensor adjustments are done and all jacks are cleared away, you can start the engine. All the doors, hatch and hood need to be closed for the AHC to work. This adjustment will yield up to 2.5" of lift in the front.
5. Now for adjusting the rear. Again, make sure ignition is off. No need to remove the wheels, just crawl underneath and locate the Height Control Sensor. There is only one for the rear. If you slide the adjustment to the top, you'll gain about 1.75" of lift. For more, you'll have to extend the mount 2" or so. I used 1" aluminum flat stock and drilled two holes (to mount to the existing bracket) and slotted a 3rd hole for adjustability. If you space out the aluminum stock from the old bracket 3/16" of so, you can get better adjustability.
6. Fill Reservoir with AHC Fluid to correct level. It is also a good time to flush the system if its never been done before. Lexus recommends a flush every 60k miles. How to flush AHC fluid thread: Changing out the AHC suspension fluid? - https://forum.ih8mud.com/showthread.php?t=60619
After you get the height you want, you'll want to get an alignment job. If you haven't already installed a differential drop bracket, now is a good time.
About AHC HI/N/LO modes: if you raise the front 2", you'll still be able to go into HI mode. If you raise the front suspension 2.5", the AHC system will raise and then come back down to N mode. I suspect the suspension is "topping-out" and so it reverts back to N mode. However, you'll be able to adjust to LO mode at any lift height.
I noticed a slight increase in ride firmness. I'm not sure if it is because the increased angle of the A-arms or the increase in AHC fluid suspending the vehicle or if it's just all in my head. But the Ride Comfort adustments work fine after this mod.
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Edit: Perhaps more important than the amount of lift is the amount of droop left in the suspension. If you lift too much, your suspension (shocks) will "knock" (top-out) when going over bumps. Here's some advice from ATS4X4:
You should maintain a minimum of 70mm [2.75"] of droop in the 100 IFS front set up, if you have a Slee diff drop fitted, to stop the cv boots wearing out. [boot pleats shouldnt be touching in straight ahead position at ride height]. This is normally 50-60mm higher than standard, depending on accessory levels. On a 16" rim this makes for 770mm [30.3"] measurenent from bottom of rim bead edge up through centre of wheel to fender edge when set up correctly. Rear should be aprox 790-800mm [31.5"]
banana: job). You'll need to furnish/fabricate a simple bracket extension which I'll cover in step 5. You'll also need one can of AHC fluid from Toyota $22/can. (part # 08886-01805). I have heard the exact fluid costs more if bought from Lexus.1. Take measurements of your ride height at each corner of the vehicle. I recommend measuring from the fender lip to the bottom wheel lip.
2. Turn off ignition. Locate the Height Control Sensor as seen in the diagram. Note the position on the adjustable top mount. You are going to want to slide it up as far as possible in the next step. For better access to the height control sensor, you can turn the wheels full left/right.
3. I found it easiest to just remove the top nut of the heim joint (10mm) and adjust the rod so that it is as short as possible. This will give you about 2" of lift in the front. If you want 2.5", you'll have to shorten the heim joint (I used a cut-off wheel) and then used the existing stop-nuts to "smooth out the thread" and actually remove the stop nuts completely. Be careful because one side is a reverse thread. Not many people I know have a reverse cut tap/die set.
Once done, reinstall the heim joint and adjust it so that the Height Control Sensor lever is as high as possible. Remount the wheels. You can readust the sensor through the wheel-well later. Make sure ALL adjustments are done while the vehicle is OFF for safety reasons!
4. After the front sensor adjustments are done and all jacks are cleared away, you can start the engine. All the doors, hatch and hood need to be closed for the AHC to work. This adjustment will yield up to 2.5" of lift in the front.
5. Now for adjusting the rear. Again, make sure ignition is off. No need to remove the wheels, just crawl underneath and locate the Height Control Sensor. There is only one for the rear. If you slide the adjustment to the top, you'll gain about 1.75" of lift. For more, you'll have to extend the mount 2" or so. I used 1" aluminum flat stock and drilled two holes (to mount to the existing bracket) and slotted a 3rd hole for adjustability. If you space out the aluminum stock from the old bracket 3/16" of so, you can get better adjustability.
6. Fill Reservoir with AHC Fluid to correct level. It is also a good time to flush the system if its never been done before. Lexus recommends a flush every 60k miles. How to flush AHC fluid thread: Changing out the AHC suspension fluid? - https://forum.ih8mud.com/showthread.php?t=60619
After you get the height you want, you'll want to get an alignment job. If you haven't already installed a differential drop bracket, now is a good time.
About AHC HI/N/LO modes: if you raise the front 2", you'll still be able to go into HI mode. If you raise the front suspension 2.5", the AHC system will raise and then come back down to N mode. I suspect the suspension is "topping-out" and so it reverts back to N mode. However, you'll be able to adjust to LO mode at any lift height.
I noticed a slight increase in ride firmness. I'm not sure if it is because the increased angle of the A-arms or the increase in AHC fluid suspending the vehicle or if it's just all in my head. But the Ride Comfort adustments work fine after this mod.
---------------------
Edit: Perhaps more important than the amount of lift is the amount of droop left in the suspension. If you lift too much, your suspension (shocks) will "knock" (top-out) when going over bumps. Here's some advice from ATS4X4:
You should maintain a minimum of 70mm [2.75"] of droop in the 100 IFS front set up, if you have a Slee diff drop fitted, to stop the cv boots wearing out. [boot pleats shouldnt be touching in straight ahead position at ride height]. This is normally 50-60mm higher than standard, depending on accessory levels. On a 16" rim this makes for 770mm [30.3"] measurenent from bottom of rim bead edge up through centre of wheel to fender edge when set up correctly. Rear should be aprox 790-800mm [31.5"]
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