Ok cool - right place at least.
There is a sweet spot that you can usually find by ear, but I'm not going to try and even put it to words for fear of getting torn apart by others. So I'll go with the probably best to get a CO analyser on it and set the mixture up that way. Going to the extremes of either end definitely shouldn't be required tho - outside of a fairly small range the car would die on lean/richness alone from fiddling with that screw.

Think we're going to need some background of where this issue has started. Was it fine then just stopped idling? Is it just idling badly or does it just die (both hot and cold)? Even when its idling badly, if you apply throttle does it then pick up cleanly (I know you said 2k onwards is fine, but from idle to that?)? Cars modified - with what exactly?

These engines aren't difficult, but people have a habit of not understanding them too well so things get "fiddled" a bit too much which can make it a pain to set right blindly.

Basic things I check on any MFI assuming it hasn't been sat in a barn for months or years without running, not in any particular order:
Vac leaks
Fuel filter changed recently (~6months)
Ignition timing
Cam timing (bear in mind if this is out or you change it, it will alter ignition timing)
Rotor arm and dizzee cap in good condition
Fuel pressure
Fuel Mixture
Plugs
TB adjustment

Again some of the above will impact other things. Alter cam timing and you'll move ignition timing, alter TB setting will impact mixture etc etc so its just a case of going through it logically.
Things like coils or the distributor unit can and do go, but they are unlikely to cause poor idle only IME