my cousins 92 si revs up and down to 2500 rpms when idling. its giving a 14- idle air control (iac) valve, 3- map sensor, and a 23- knock sensor trouble code. i know there's a number of things that could be wrong. I think it is the iac that is messed up and maybe throwing off the map sensor. any suggestions of where to start?- no aftermarket anything