I've just been back through all the answered entries in the cars section back to October and I can't find any previous question that ties up with your question!! so I would suggest you start from the begining, with the make/model/year/engine size & type and a full description of your problem, there are some very informed people on here giving out free advice but to my knowledge none of them are mind readers!!!!
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix cars.