hello mark just brought a c20let corsa.

it started hunting when you pull up and mark phoned the old owner and he says its the idle control valve, but its only raising the revs by a few hundred rpm and as it hunts the dump valve is fully opening and closing?

mark says he thinks the dump valve should not do that, should it?

we know its over fueling on boost but mark thinks the dump valve might be sucking in air when its driving? due to as soon as the revs raise even the slightist its fully open?

comments please mark just wants to get it sorted before taking it for a set up.

spec is
phase 3.5 chips
evo 4 td05 turbo (custom down pipe and side exit)
200sx tubular manifold
rebuilt engine with xe inlet cam
saab red injectors
60mm top hat and hard pipes
frontera 2.8 intercooler (which is being changed)
8v baffle plate
got a rolling road print out for 291bhp at 13psi

but we think this problem and the intercooler is restricting it?

thanks