bit of a weird probelm i am having on my 4x4 saph cosworth

the ABS light goes out fine after start up but then comes on sometimes while driving along, could this be a faulty sensor?

i've also recently just started to get pulsing through the brake pedal when pressing the brake for the first time after a couple of mins, if i press it straight away again this doesn't happen, but if i leave it a min or two, like when driving, the pulsing comes back

any ideas?

cheers Matthew