Hi,
My toyota camry conquest is fitted with LPG.
When i drive with LPG there are no problems.
But when i start with petrol, the engine vibrates while idle, the RPM jumps up and down continuously from 600 to 800.

Would a tune up fix this? and how much should i pay for a tune up?

I have no idea how they switch from LPG to gasoline, but for regular gasoline powered engines spark plugs, wires and distributor cap are very important maintenace items. As well as air filter and clean MAP/MAF sensor.

Good luck,

Sam