2004 2.4 Accord stalls at idle...

2004 2.4 Accord with LPG. The car drives lovely but when pulling up to lights or a T junction, the revs drop and don't stabilise normally. They just keeps falling and then the engine cuts out so it's a case of riding the clutch and keeping the engine going whilst I stab the brakes or use the handbrake.

So far, I've paid 4 garages to have a look and so far have been told it's the battery, ECU, O2 sensor and to get Honda to reset the computer, which they won't do, so no one can find the definitive problem, just come up with expensive things to try. ARGH!

The ABS lights are on now too but this idling problem was on before that light was on so I'm not sure that's the problem.

I've changed the battery and the O2 sensor and the problem is still there. It doesn't matter if it runs on LPG or petrol, it still does it.

The ECU is an expensive part to swap out just in case that's the problem. Could it be the MAF, the idle control valve, could cleaning out the throttle body help...?

Any advice would be very much appreciated.

Cheers.