what u mean they adjust timing with a screw driver, timing is never adjusted with a scre driver, u use wrench to loosen ur distributor and then changes its angle.
Air fuel ratio is altered in non efi cars using screw driver.
In cng kit there is a screw to change pressure of gas going to engine
And then there is a nut on main hose that supply gas to engine which change the amount of gas flowing in to the engine.
If u car do not have adjustable distributor then u must go for tap other wise adjusting timing and other parameters is the only choice.
By the way for most of the cars almost all the cars that I have 1K rpm is normal idling speed, as u have said ur car now idles at 1K rpm then thats no problem.
