1995 Vauxhall Tigra

Hi I brought my wife this car a year a go now and have had constent problems with the performance I have spent 100`s of pounds to put it right with no avail. It coughs and sputters and no power but starts first time. The engine managment light comes on. So took it to a garage and he said it was a valve in the engine which carbon builds up a lrg valve or something like that he linked it to a machine. So had that replaced. Spark plugs brand new. And still same prob.I have read a few forums and 1 guy said try replacing the The coolant temp sensor? And also smells of petrol now and agin? Any ideas would be very helpfull thanks

Mr D rowley.