Throttle sensitive cold start 1999 Vortec 5.7

[Pinger]

I'm going to wind it back in with the engine hot and if the IAC compensates then hopefully progress. If I do it cold it will just die.

Did the above yesterday and the idle speed didn't move initially but then came down from 900 to 500 rpm on the tach (which over-reads) so stopped winding out the screw at that point.
Cold start on petrol today without pedal no problem. Switching over to LPG is a bit erratic now though cold or hot.

My suspicion is that in the LPG conversion it was messed with - or in a subsequent attempt at getting better running on LPG when what was needed was a service.

So, looking like the screw has been moved as a compensation for LPG.
On LPG everything passes through the throttle body - air and LPG in vapour form. At start up, the LPG mixture is rich and will easily be adding 10% of volume through the throttle body compared to running on gasoline. This figure may have risen lately due to the (self learned from O2 sensors) default having gone higher (it is that default setting that is utilised during start up).
I think I can try extending the switchover period where both fuels are momentarily supplied. If that doesn't improve the switchover then I suspect I'll have to open the butterfly a bit again.

You seem to be on the money Schurkey re gasoline operation. It's just the LPG complication that I'm going to have to compensate for. But I'll try and land at a point where it's more like it should be for gasoline - ie, screw out and let the IAC valve do its work.