I have a 02 astra that has intermitent misfire.I have had new coil plugs and compresion test.still misfireing, have done the brake throttle test and came up with err!codes po304 0300 0302 0400 help!

william, March 2012

P0400 refers to the EGR valve which, if faulty, can cause the misfire.
You could either remove, clean and refit the EGR or buy a new one. If buying new make sure you buy a good quality branded part, some of the cheap copies are rubbish.
It is possible to blank off the EGR using a blanking plate but this will probably put the engine management light on.

frank, March 2012