I was always taught, think simple, basics first. Think about what can keep engine speed up. It has to be either additional air or ignition timing just like non EFI. What air paths are there at the thottie body? Throttle blade, IAC, more? How about the PCV sticking open? No air source found? Then go to timing. Can you monitor ignition timing on your scan tool? Once we know if it's additional air or timing the next step is to locate why the change is being commanded. Find what is causing the RPM increases first.
Doug