the p1574 code is down to your braking system if i am not mistaken
Brake pedal position (BPP) switch - circuit malfunction
for the code to come up the conditions are as follows
A 2.5 MPH or greater decrease in non-drive wheel speed in 0.4 second and extended travel brake switch or TCC brake switch indicating brakes applied and no transition noticed in the stop lamp contacts of the Stop/BTSI/Cruise brake switch.
i suggest u start looking at fuses first
it is not throttle body related
the problem is your braking system is hooked up to your abs system that is hooked up to your traction control system, it could be your tc messing about as to why u are getting spluttering problems
your best off asking vocky about fuses and relays concerning the braking system
i suggest u get an obd2 reader and do this
http://www.hotrodlane.cc/New%20LS%20Lin ... 178&evc=sm
this is what vxhall will near enough do but at a cost of a hundred quid an hour, i bet is more likely to be a fuse so i suggest u u check your fuse box and the fuses in the engine bay but ask vocky for help
if your abs light was coming on as well then i would of said it is an abs sensor and vxhall didnt pick up any other codes apart from p1574