my mate has a VZ and just today it has started running on three or four cylinders, i am guessing plugs since he doesn't think they changed them when he had his last service done,
codes??? could be anything, coil pack. doubt plugs is more than one cylinder missing.
in relation to codes, if theres no warnings on the dash saying something like, check powertrain or something...all you do, is have your car turned completely off, press the mode and set button at the same time and turn ur key to accessories...the dash should display from memory " GM part number (whatever the number is)"..i may be wrong...use the mode button to navigate through this menu, you will find useless stuff in there..and don't be afraid when ur whole dash lights up and everything is set to half way, this is just a check...im pretty sure the last thing is the trouble codes, if there's no codes it will come up with lots of 0's...otherwise there will be a code such as P0562 or something, if a code comes up, post it on here or email me at email@example.com and i'll let you know what the code means and possibly how to fix the code/fault