I installed a lightweight chrome moly flywheel (lighter then stock). not as light as the aluminum ones, I think its around 10-11 lbs.
like I said before, could be the base idle settings needed to be adjusted. (biss screw, special procedure to set it, check VFAQ)
also noted when working on the car that you have a 2G MAF with stock 450cc injectors with no sort of fuel management (that I know of)
this will make the car run all sorts of weird, run either super rich or lean, the 2g maf flows more air then the stock 1g maf, so if you change it you have to go to 550ish cc injectors to make it run correctly. Or you could use a MAFT or safc, or get a eprom ecu and tunerpro RT, or DSM link/jackel/werewolf this could be causing most of the problems and is now more noticeable with the lighter flywheel