starting issues and loosing oil

Please help! I bought a megane 1.6 16v 04 around a month ago, perfect on 2 test drives no unusual sound etc. On drive home car went into limp mode and toxic fume light flashed, garage said misfire on cylinder 4 so coil changed, car was fine. Then starting issues, car make a grinding noise if not going to start and will start first time if revved for few seconds, then when cold very juddery for awhile until warm, Judders when idleing and rev counter can be seen moving slightly whist doing this, sometimes only sat for half an hour or so before not staring again ( have read up on dephasher ànd not quite my symptoms) tdc cleaned up, no different. Sometimes sounds like diesel engine and sounds like it is struggling when being driven, other days drives fine. Another problem is it is loosing a fair amount of oil with no visible leaks. Is blowing smoke from exhaust looks white to me, hubby says it looks slightly blue, Have done spark plugs, oil filter, waiting for new ignition coils to come have checked for head gasket signs, can't find any! Car has stalled a few times, spoke to a garage who said that thought there was two different problems but would charge a lot just to look, some one else said piston rings so new engine and also toxic light has started flashing again! Please does any one have any ideas? Hubby will have a look at weekend buy does any one knowwhere to start! Thank you