Hello, I have an issue with my 1997 Chevy Suburban with 5.7 Vortec and dual fuel conversion, 215k kilometers: it developed a consistent rough idle since a few days that started when driving in very rainy weather, but it does only do this when running on LPG, not on gasoline. On gasoline it runs very smooth. Hot or cold makes no difference. Any idea where I could start with the troubleshooting? I also hear a very distinctive tick once every revolution when it is idling rough, sounds a bit like a noisy valve. But when on gasoline there is no noise. Any thoughts on where to start? Thanks!