Rough runner help

Hi all my 4.6 rangey Thor engine with omvl LPG is a little sick
It starts first time every time but when the revs come down to under a 1000rpm it starts to go up and down and sound and feels very lumpy and occasionally stalls but doesn't do it all the time some days runs fine but some days it coughs and splutter
Seems to run on LPG fine most of the time
Could it be the maf censor and how can I check if it's faulty or could it be something more serious
Also have a small hole in centre exhaust
Can anybody help please thanks

MAF or Idle Control Valve...

When were the fuel trims last reset??

Mine ran rough when I first bought it - especially when the weather was damp, so I bought new plugs and leads and started to fit them and then discovered that the previous owner had not pushed the leads onto the plugs properly - pushed them on and it ran sweet as a nut - I still changed the plugs and leads as I had bought them but it made a huge difference.

Darren

Possible dodgy coil pack.

What is involved in resetting fuel trims and where is idle control valve