Noticed my economy on LPG had been slowly dropping recently so i decided to replace the plugs (well past due), now ever since it has idled rough. Thought I may as well change the leads, dizzy cap and rotor, all of which I discovered was well overdue.
First time I tried starting it took a few tries and once it kicked over a big plume of white smoke came from the exhaust and took 5-10 secs to clear up.

It runs better but still idles like crap.

Any ideas?

It runs fine on petrol.

Its a Vialle system.

Something on the gas side will be out of tune.

The new parts will obviously work much better but the system would've been tuned to run with old s**t spark.

Pretty sure the ECU can adjust the fuel side (to a degree).

Sounds like you've disturbed a hose/line on the LPG side - balance, etc.
Dislodged any of the induction piping ??? Sucking air through the hose inlet under the throttle body ??

Seeing its a factory Vialle Gas setup (though dealer installed) I tried the factory self tune function and everything worked fine and the car runs better than ever! Havnt driven it enough to gauge economy improvements yet

I used this procedure.

http://www.fordmods.com/forums/download.php?id=16284