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Anti-lock brake feathering. Toyota Highlander.
Hi ... 2002 Highlander, in-law hand-me-down. 
When starting up at very slow speeds (< 5 m.p.h.), the ABS system starts to "feather." I can't describe it any other way, other than to say it feels like the ABS system is kicking in. Since my foot is not on the brakes, I can't feel it there, but the ABS light on the dash does light up, and it makes the familiar sound.
It happens intermittently, and never at any speeds other than a very slow one, and trying to accelerate, especially in a parking lot.
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Comments
Sounds like the ABS self test. Often you hear a bit of "shudder" or "clunk" and sometimes if you rest your foot on the brake pedal, you can feel a "shudder", but it depends on the car. If that's what it is, it's completely normal.
I've read that some cars won't do the test unless the car has been sitting for several hours but I thought the self test happens every time you restart your car.
This self-test should only happen the first time you start up. If you're saying you hear it every time you stop in traffic and start up again, then something's wrong with the system.
Right, I don't think it is a start-up thing ... it happens both when warm and cold, but only at very low speeds, and only when slowly accelerating, and only very occasionally. I do know the ABS light comes on when it flutters.
Could the ABS be kicking in because it is falsely detecting a wheel slip, thinking it is actually a braking problem?
Quite possibly. It would be good to scan the sensors to see if any of the wheels are sending bad data to the control module. Sometimes the sensor get dirty, or they 'back out" of their holders, or a tone ring cracks---
Mr_Shiftright nailed it - bad data due to the sensors having backed out of their holders. The deviation is enough to send bad data from time to time, but not enough to happen very often.
The work though is complicated by a case of rust. The Highlander lived by the shore for about ten years, and it picked up a lot of rust as a result. The shop quoted a price of $2K since the parts have to be drilled out because of the rust. (2K includes replacement parts and everything)
So now the question is ....
What do people here think of disconnecting the ABS system?