High Revs??

Hi could really do with some advice. I have got a P38 which runs on LPG. The revs have been a problem for a few weeks and after speaking to quite a few different people I am still stumped. When starting it the revs climb from 1000rpm to 3000rpm. If you put it in 1st gear and release clutch (as if to stall it but not quite, just to drop the revs) the revs will lower but not always. Once the engine is just past middle on the temp gauge and you have driven it for a bit then the revs seem to stabilise but not always. When working on the car it is hard to gauge because when I think I have solved it and then drive it or leave it cool and start it again the problem is still there. I have changed the throttle body, the throttle position sensor, checked all pipes etc and everytime I change something it seems to sort it then it gets worse again. I have been told it could be the idle air control motor - could it be anything else or does this sound right?

Before I got to the end of your post I was thinking idle air control valve....

What year is yours as the engine changed throughout the P38's tenure!!!!

It is a 1995 4.0 V8 manual.

Then, yes, I'd be looking at the IAC valve!