dont gat disheartened mate the rs is worth keeping! i would fistly check the voltage at the fuel pump should be an absolute minimum of 8 volts if this is ok i would get the ignition timing checked also check the distributor cap and leads as it sounds like it aint firing right it will be worth checking all vacuum pipes for splits and leaks including your boost guage as these are known to leak boost also!!. also i would consider which tuner i used to set it up as i would only use a tuner that was used to rs turbos as they can be tempermental at the best of times and are best looked after by someone who knows these cars inside and out