1999.5 1.8T -- is ECU under large black plastic piece that runs across back of entire engine compartment? How do you remove the black plastic thing to get to the ECU (presumably in the back of the driver's side)?

Yes,go to FAQ section,I believe it shows you step by step, if not, I think www.goapr.com will show you

APR site just shows some little black flap over ECU - doesn't look my car.