My freelander 1.8 2001 petrol has some major problems. its in my local garage with a poss head gasket failer + 24 fault codes now the garage is saying this is why its running so poorley not the HG problem. for the last 12 months the engine management light comes on with a missfire on cylinder 3 then will drive for 500 miles with no problems over the last 2 months it comes on when i stop at traffic lights thens ist ok again this happens more frequently when its raining the green down hill light is also on for the first few miles of my journey. its had new plugs new leads both coil packs replaced its now going to auto electricain to find whats up. any idea what the problem could be