Like stated above, Check your TPS.

The BAC valve being removed will be your most likely culprit on not wanting to idle well, did it also have the dashpot on the back of the TB removed? This stops the throttle from immediately slamming shut when you let off of the throttle.

The car model and the motor model do match, correct? (S5 to S5?)

Almost all rotaries run rich on the stock ecu. If someone else did the swap, I would be sure to check and make sure the correct injectors are in the vehicle also.

Just a few tips. If you need to know how to set the TPS, ill link the FSM for ya.

- Chris