Weird RPM drop then increase while coasting

[fudge12]

Hello everyone! It's been a while since I've last posted since I've sold my LS, but luck has it that I stumbled upon another with lower miles and better condition. However for the past few days I am noticing that while I lightly tap the brake pedal to slow down just a bit while coasting down the highway, the RPMs would just dip and shoot back up again. I do have the CEL on for Bank 1 sensor 2 o2 sensor, and brake pedal switch input (secondary brake switch).

Attached is a video, you can see the drop and increase toward the ending. Is this something normal that I just haven't noticed before? I don't recall this happening on my other LS.

Video.MOV

 

[joegr]

If your brake switch or brake switch input isn't working, then the PCM won't know to unlock the torque converter as you start to brake. I can see that causing a drop in engine speed till it gets low enough for the PCM to take action anyway.