Small update: No vacuum leaks and the throttles close completely. When I blocked the ICV, the engine stopped running unless i opened the throttle a little. So the too high idle is controlled by the ICV. I'll remove the ICV and test that it functions as it should. Otherwise we're most likely looking into software problem or something funny with the air mass meter. I got INPA running on another laptop for a while but the next time powering up it barely started, had lost the driver for the cable and wouldn't accept it again. Time to dig deeper for that one ancient laptop I have with Windows XP in it.