2003 Vauxhall Zafira dead spot and eratic idle speed

There is a dead spot on the accelerator when starting off, I put my foot down in first and the engine nearly stalls unless I give it more gas. Also the idle speed is eratic, at rest it revs from 750rpm to 1000rpm almost as if I am pressing the accelerator. We have had this for a while now. Have had engine management changed, new water pump etc. Also temp gauge only works when the engine is off and ignition on, when moving it drops to zero.