Turbocharged 98 LS

i just turbocharged my 98 LS with a Greddy GSR turbokit..with sum adjustments..it works and runs..but it idles at around 300-400 rpms and jumps up and down..and sometimes it shivers violently..and wen its running..it cuts off at 6000 rpms..the engine maintenance light is also blinkings and annoys the crap out of me...and also therz this nasty rattling sound wen i shift at high rpms..could i get rid of this wit a blowoff valve??
thanx