if its still playing up re-install stock ecu and hook up a diagnostics tool to it, ask mercury or what ever shop u use, one should have one and it should be able to pull out a fault code, letting you know exactly the fault, my guess will be afm's most likely. very common problem, they just get old solder inside them and can be repaired, but most people exchange them or buy new ones at great expense. butr could be another issue with iac aswell? try them all, just go to the diy section and start searching for HOW TO: threads. its a process of elimination with skylines.especially when it comes to sensor problems, some or many may lead to the same out come, its just trying to find the correct one which is a bitch.