Startup revs not right still !!!!!

Ok engine is 4.0 thor . Ive just replaced the engine temperature sensor and the reading is more constant as it was all over the place before. Ive put back my original idle control valve but im still getting this revving upto 2000-2500 revs sometimes on startup and eventually down to tick over. Ive plugged in the LPG software and alls ok there and also tweaked the pressure upto 1.5 bar on the rail(starts on petrol for a while before chhanging over). Im wonderingif its the crankshaft sensor (not the cam sensor)
that might be on its way out . Runs fine no stalling , its just on startup where the revs climb until i blip it and all goes to normal. Its anoying me now

Turns out to be the replace throttle position sensor. A new set of plugs and she roars again

We all knew that!