High idle regardless of whether it is cold or hot

[fixkick]

the LPG, must change lots of things... i'd bet it's not just LPG injection added to the air horn.
lots more... to it, than that.
many LPG kits, have added an air VALVE (Idle speed control device) to one of the many possible vacuum lines or ports. on the plenum.
all this is a custom modification to a stock petrol car.
and there are many makers of kits, all very different.

it also cuts petrol fuel some way.
and monitors spark some way to be sure LPG does not flow on a stalled engine or after a wreck.
my guess, is it uses its own added MAP sensor to calculate LGP flows.
some add and EGT exhaust gas sensor to regulate LPG flows,

if the LPG mode, fools the ECU, as it surely will
the ECU goes to limphome mode.
retarded timing, and idle controls dead.
i bet the ECU is complaining big time, in LPG mode, ever scan it to see that>?
DTC codes, 13to 53. on this ECU. 12 is normal.

http://www.fixkick.com/ECU/DTC-errors/DTC-jtgh.html


here are the limphome rules
Ive never run test like this. (but have done this on a bench)(
http://www.fixkick.com/ECU/LimpHome/failsafe.html
but I'd say with car started in LPG mode.
the ECU thinks car is push started, or was started by coasting down a hill and some one released the clutch and is now running,
It injects fuel when you do that so, id bet LPG has fuel cut device there, preventing that.
the ECU would get real lost like that, unable to control fuel at all, in anyway... and go to limphome mode.

It all gets down to one fact, how to fool any OBD1 Petrol stock ECU..?
In petrol mode your idle controls are failing 800 rpm is hot RPM, AC off.
So why not insert the diagostic jumper see if there is a DTC code.