My 03 V8 Limited has also had issues with the rear air suspension system.

Much like MacVay who started this thread, my T4R also experienced the back-end jack-up (like a hot rod at a drag strip). To my surprise, it had the nerve to do this while at the dealership for an oil/filter change.

Diagnosis was a corroded sensor (due to the road salt from our Canadian winters). Cost to replace the sensor was too high for my liking (and knowing that this would be a temporary fix at best ... the issue of the vulnerability to further corrosion of this sensor in the current location having not been addressed).

Initial repair involved bypassing the in-cabin height adjust controls and securing the air suspension at the normal height, then shutting the system off.

Since this repair, there have been two occasions where the air suspension deflated (no real explanations for this) and I was basically driving with no suspension (think horse and buggy or Model T Ford).

Most recent repair was, much like CJ3Flyr suggests, to use the existing wiring from the rear air suspension to the height adjust control switches, but remove the auto-leveling feature.

Basically, I can now power on the system, and use the in-cabin switches to add air to the rear suspension to raise it up. But I have no switch control to dump air out. That has to be done manually.

So my rear air suspension is working, although not as designed by the Toyota engineers.

Future repairs might involve installing aftermarket air suspension (Firestone as CJ3Flyr suggested) or removing the air suspension completely and installing rear coil springs.

My real world driving experience with this air suspension system has been less than satisfactory. I will avoid such a suspension option on any future vehicles I consider purchasing.