bouncing/hunting idle on LPG when lifting foot off the throttle

Hi all

I have a intermittent problem with my disco 3.9 V8 LPG.

Sometimes it idles way too slow on LPG, almost like it will die when slowing down to a junction, goes to 850-500 once I stop for a minute it picks up again to around 800. but sometimes the CHECK ENGINE LIGHT comes on saying low fuel pressure. This ONLY happens on LPG, apart from that it runs fine.

Could it be the Throttle position sensor, is the pressure within the vapouriser needing turned up a touch?


Thanks in advance.

I’m no expert on these systems, but I’ve learnt a hell of a lot having one fitted to my 4.0 V8!

Some questions that may help pin down the fault a bit:

Is it a sequential (multi point) system or the older inductor vaporiser system?

Some thoughts on simple things to check would be:
* have the vaporiser filters been changed recently?

* some vaporisers have a vacuum line attached to the manifold to help them adjust the flow of gas (pressure) dependant on engine load - do you have one, is it connected, is it blocked or cracked?

*When was the system last serviced?

*have you changed anything else on the car or engine or changed service stations recently?

*has this fault suddenly developed or has it started and got worse, or has it always been there?

Maybe there is something helpful in there, if not, then maybe it will help narrow a few things down!

Tartarini SGI multipoint system, serviced in December, had new injectors inc filters fitted and both lambda replaced. This has only started since it was serviced. Garage will not entertain taking it back to look at without charging me for the privilege.

There is your answer.

I'm surprised you needed new injectors, I've run loads of lpg cars for massive miles, and never needed to change an injector.
One lpg kit I had, was taken out of my 140k mile Saab, having done about 90k miles, and went on to do another 80k miles in another Saab.
Never had an injector or lambda go.

Apart from taking it to someone who would seem to care about their work!

All I can think of is the small bore hoses from the manifold to the vaporiser and the pressure sensor. Check they are connected.

Could be ignition timing / vacuum advance

Vacuum advance unit ?

Vacuum advance pipe to from plenum to distributor assuming it is using a distributor. If it is holed it would show up the LPG running more as LPG requires more advance. Timing is often overlooked by LPG garages. I'd check it, advance if poss, avoiding pinking on petrol and reset base idle when done.