I have just purchase a 1996 XH XR6 Ute and the.

I have just purchase a 1996 XH XR6 Ute and the revs fluctuate when idling and also on braking. It seems to spike and then drop back to about 650 rpm idle. Also at points of idling when stationary a large hum or vibration goes through the cabin, which goes away if I put the ute in neutral. I have cleaned the throttle body, TPS and put in a new fuel filter, however this hasn't inproved the situation. In fact I have noticed that when first starting the ute and applying the accelerator there appears to be no power, I have to back off the pedal and apply it again to get it going. It also pings under load though I have had a mechanic (who completed a roadworthy on it about a week ago) look at it and he said the timing is perfect. Any help would be appreciated.