106 idling problem

hi my 106 (xsi 1600cc 8v 'n' reg)
shudders when idling, the rev counter bounces up and down and it sits on roughly 800 rev's,
when not warmed up it stall's,
i have a device fitted to trick the air temp sensor, when this is turned on the problem is better but not fixed (it sit's on higher revs)
when the throttle position sensor is disconnected the problem is fixed but the car drags after first gear and will not accelerate
now and again then problem fixes itself but very rarly when this happens the engine temp is usually just below red
any help would be appreciated thanks
ashley