I once owned a '79 280E, the '80s are somewhat different so my advice may NOT apply here.
I recall a rather large (2 cm) white plastic or nylon set screw - head slotted for a large flat blade screw driver. This is located on left side and seen from the front of the engine with the air cleaner removed. This screw is the idle speed air control and is what you need to adjust. This engine should idle about 700 RPM, in Neutral.
Can't help you a bit on the LPG question - Rob Smith may be able to.
Sorry T.G. I've no experience myself with the LPG, Tho from installations I've seen, there's not a lot of adjustment on the gas governor, apart from the spring pressure and an adjustment of the gas flow (usually a large flat headed slotted screw, that's about it). The gas is also heated I think to remove the effects of the expanding gas cooling the inlet too much and 'freezing'. I will speak to a friend at work who is going to fit a DIY kit onto his Stag, and has gone deeply into the LPG stuff.
Sorry. Rob.
"T.G. Lambach" wrote:
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