I have a newly rebuilt scion tc with about 20 miles on it and its just sitting. I havent been able to drive it because of no tag insurance ect. The problem im having is when i start it. The first thing to heppen is it will idle about 1500 rpms for about 15 seconds. Then the idle will drop to 1000. In the next span of a minute or so,the idle will bounce from 2000 to about 1000 and fluctuate. Back and forth. Ive cleaned my old intake. The intake tubes, the maf, and throttle body all have been cleaned. It throws a code for random cylinder misfire on all 4 cylinders. Not just one. Its got new plugs but old coil packs. It has a code also for running too lean. Given the only mods this engine has is a performance header, it kinda stumps me. Ive never had this kind of problem before. It has a half of tank of super because of the plugs im running. Ngk iridium plugs. It sat for a few months and i even put fuel treatment in the gas when i got the motor in. Any ideas or anything i should change out?