Has anyone with LPG experienced this or have any ideas?

After getting my Magna serviced (here (http://www.aussiemagna.com/forums/showthread.php?t=70534)), I"m getting this annoying shudder while idling in gear on LPG. Everything's smooth on petrol and while the car is in motion on LPG, it's only when at the lights this annoying shudder occurs.

Any idea what's causing this? Got my mechanic stupped - & he's not familiar with lpg systems.

Is it because i'd had the spark plugs changed now they're sparking better so I'd need a lpg retune for the update air/fuel mixture that was set for worn spark plugs? I've got the basic system so it's not real intelligent, with a premapped idling set point.

what happens is the idle set becomes loose and it changes over time. After you have a LPG system put in a car you need to take it afta bout 1500-2000 ks to get it retuned to idle as it starts to become really rough because the spring loosens up after being brand new... Then afta about 20,000 you need to do this again, well not really 20,000 12months which evre comes FIRST - oh and you need the LPG filter changed, YOU WOULD BE SUPRISED THE RUBBISH YOU FIND IN IT. go to a person who converts cars and ask them for an LPG service just to retune and change the LPG fileter if you havnt done that. ALSO if you have put any MOD on the car, you need to RESET THE ECU by takign the neg cable off the battery--- that fixed my cough at idle after puting a exhaust + extractors, started coughing as soon as i put the exhaust- so just try teh ECU reset... then if that doesnt work take it and get a LPG service

Is it a mixer system? There's a couple of knobs on the mixer for adjusting the idle, work out which one is your idle and just adjust it till it doesn't shudder anymore on idle.

The spark plugs could also being causing a problem if they're not specified for dual fuel cars, standard spark plugs for petrol cars don't work very well with LPG.

yea get one level colder with the plugs.

happens to me, stupid enough the car even dies! after service, but funny enough the day after onwards it runs well.
No clue. I have a feeling LPG convert has maybe brought more repairs to my car as I never had oil leaks before till LPG was installed. Sad case really.

I think you just had a bad installation - it all makes the diff. Some instalations take short cuts and dont do a good job, end up causing more harm then good. I never had a prb with lpg only with the idle when needs to be retuned, but reseting ecu cured it for me.

alot of people dont know of the lpg FILTER - keep it clean to keep good gas flow... also keep oxy sensors working that can make a gas system run really bad. If you get a backfire through your intake... (dont know the terminology for this) THIS IS A ERROR IN THE INSTALLATION OF THE SYSTEM - short cuts are taken - many companys do this...typically its the ones that charge you close to the 2000 mark.

Take it to a GOOD LPG conversion place.... and get a tune... IM SURE midas does it now... just get a LPG tune and see how it goes.