LPG on a 1990 RRC - Idle Air Control Valve

[RaginRover]

Hi Guys,

I am in the process of converting my 1990 Rangie with a 3.9 to
LPG, got it all up and running but the IAC is giving me trouble.

Basically the way I have it setup now is that I cut the power feed into
the computer (the accessory feeds not the perm power) and switch to LPG - now the problem there is that it winds the IAC Valve all the way out before it turns off and makes the gas idle at 2000rpm,

So my next thought was to cut the control wires to the IAC valve
and put a relay on it so when I warmed the car up on fuel I could cut over to LPG and the valve would stay put. ... so far so good

I tuned it up with some help the other night with the IAC unplugged and it idled at the same RPM on fuel and on LPG so it was sweet.

Currently using this method that valve seems to change
from time to time and breaks my LPG idle (stall) and make fuel idle really low.

My question is for those with a 3.9 EFI with a IAC where/how have you spliced in your LPG cut off for the injectors/fuel pump, I assume people somehow kill that part of the injection system but leave the IAC operating to adjust the idle - wouldn't that put the check engine light on ??

Thanks guys I am a bit confused now I thought I had it all worked out but it looks like there is something I have not considered.

Tom

[RaginRover]

Just for the sake of completing the forums as a resource the trick here was not to turn the ECU off but to just turn the injectors off and leave the ECU running.

The ECU doesn't mind - no error codes on this model and then you can just use two relays to turn off each bank of the injectors and wire that up to the gas change over switch.

This way the IAC still controls the idle nicely.

Tom