you can buy an OB2 scanner on ebay. A Maxiscan MS 309 it will be the best thing you have ever owned since cars had a diag port in 1996.You can even take it with you when you buy your next car,then you will be ahead of the bloke who sold you
your last car.The scanner will not always be right,but will point you to the right area,you may only need to clean what it says
is producing the fault.The MS309 will even show live data,you would have needed an oscilascpe to do this not long ago.You can get one for £8.99 and even help somebody out with a diagnosis for any car.Good luck.