erratic running & Idle

[harleyfatboy]

Can anyone please advise.

98 Grand Cherokee Oris 4ltr, converted to LPG. The car normally runs brilliant but has started to misfire and tickover is very erratic, this dosent happen all the time and can go weeks with no problem. I travelled 80 miles today mostly on motorway after about 70 miles on cruise control it occasionally missed (bit like hickups), when i stopped and came back to the car after a few hours it struggled to tick over and was very erratic. if i floor the pedal it picks up and problem goes away, its the same on Petrol and LPG, wet or dry conditions.

I have replaced leads & plugs, any ideas where to look?  :(

[Plum]

Ive not got gas on me jeep but i did av on the jag xj6 sov 4.0l an the same used to happen to me however after a time it then even started to stall (only on gas though) when breaking at a junction rounderbout off the motorway,  the fault on this occasion turned out to be the gas set up. . . . . . . .

[Bishops Finger]

Get the O2 sensors checked out

[harleyfatboy]

How many 02 sensors are there,can they be checked out or will i need new ones?