2001 octavia eml light..

[999gsi]

looking for advice.. I own a £200 shed Octavia 2.0 petrol....my commute to work is 14 miles of A roads and car runs fine...as soon as I drive in the city. stop start traffic the eml illuminates....last yr plug 4 was kaput car running badly. change it, new coil pack, new o2 sensor, light still coming on.runs fine. code reader shows misfire cyl 4,multiple cylinder misfires. i clear the codes... city driving on it comes....no loss of mpg etc want to sell the car but with eml on I will get less for it....any idea what may be the cause of this.... thanks...