Hello I have a 99 Si B16A2 and the check engine light would come giving me a p0505 IAC Valve Failure code so I replaced the IAC valve and the check engine light would still come on. When it comes on my idle jumps to 1500 and it boggles from 1500 and 3000rpm. another weird thing when my car idles normal at 750rpm i noticed when I turn on my headlights the rpm jumps to 1200rpm i have no clue whats going on any help would be good. I need advice HELLPP!!!!

 

when the car is cold "hasn't been run in awhile" take off the radiator cap, start car with cap off leave running, message the lower radiator hose as it warms up to try and work out any air that may be trapped, make sure coolant level is full add coolant if needed, there is most likely air and a lack of coolant, as for the drop in idle with lights may be your altenator is getting weak or the battery, take it to advance auto or auto zone i'm pretty sure they will test it for you for free hope this helps