I have been flying back and forth between KSFO and KLAS, everytime Im flying into KSFO this happens I'll try to explain it the best I can, ATC has me a little high 11000 ft, the only alt restriction in the fmc is at CEPIN at 3200 ft, now Im above the decent path so it goes into VNAV ALT but my speed drops all the way down to 213 as you see in the first pic, where is this speed coming from? I figured it was because the fmc knows that Im an idiot and Im to high to fast for this, but then in the second pic after ATC finally clears me for the approach, it commands the speed all the way back up to 240, I know at this point maby I should be using VS to descend, anyways I have alot of reading and learning to do, if anyone has any feedback at all to help me better understand I would appreciate it.

It's a design feature of the 737NG, intended to help you maintain the descent path. You may notice that the plane begins slowing down before you reach your VNAV T/D point, as well. Both of those functions exist in the real aircraft. Pretty neat, huh?

It's a design feature of the 737NG, intended to help you maintain the descent path. You may notice that the plane begins slowing down before you reach your VNAV T/D point, as well. Both of those functions exist in the real aircraft. Pretty neat, huh?

Um...yes!!!

Holy cow! That's all I've got to say about that....Adam

Completely correct behavior - this is called "energy compensation mode" - read about it on FCOM 2 page 11.31.30 (page 880 of the PDF)

Oh trust me I knew the behavior was correct just did'nt know why I still trying to read the FCOM while trying to fly, not the best scenario for something so complex, thanks alot guys, man this thing is so dam cool.