What has been rewired? Like it has a "custom" harness for the stock motor and ecu? The easiest way I see you getting it running perfect (if the compression of the motor is good) would be to just buy a new *used* non-turbo s4 emissions harness (engine harness ). Swap in the appropriate electronics including a s4 boost sensor (n326 or equivilent) and you can run the s5 intake manifolds with no problems. Basically the only thing you would be using that is from an s5 would be the upper and lower intakes.