hello all please help, when i start my car after about 3 or 4 mins the revs go up to 2000 revs then after 1 min goes down to 1000 revs then after 2 mins goes up to 3500 revs and stays there then when i switch of engine and try again it wont start. i took it to garage sat picked it up tues they said they could not find anythink the matter with it any ideas 
