2002 Vauxhall Astra engine performance not good

my astra failed its emissions on the mot so i left it parked outside my house i brought a new lambda sensor new spark plugs its got leaks in the exhaust and i have left the car standing for about a month i went to start it wen i replaced the spark plugs and it started clunking it makes a poipping noise it reves up nd down i driven it aswell to get clean petrol for it and when i put my foot down it started pulling bk ass if it doesnt wana go any faster and wen i went on the carridgeway the max speed it wanted to do is 40 the engine management light is on aswell but b4 it was ok it has only started to mess up since i left it nd replaced the lambda sensor any help ill be really gr8ful thanks matt