Check eng light is on two trouble codes show 1505,1507,the vehicle idle low when cold and high when warm. 1505 mean that idle air control valve coil opening voltage is low,1507 is the idle air control valve coil closing voltage is low. i replace the idle air control valve. the problem continues. i also eraise the trouble codes but the check eng light comes back on in 30 seconds. my question is how can i resolve this problem? i would also like to know where is the censor that sends the signal to the computer and lets it know the eng is hot or cold?