Question1999 Tiburon, car idles and starts normally when cold. After driving, sometimes when stopping at a light the idles surges up to 2000rpm then drops to 1500 and back up etc, this continues 2-5x then it will settle to a normal idle. I've changed, both O2 sensors, Trottle position sensor etc, no vac leaks. Is it the Air idle control valve?? cleaned the throttle plate as well. Any ideas?
AnswerThe revving up and down you describe is a characteristic of the computer strategy to control engine speed if unable to do so with the idle actuator.
A faulty throttle position sensor would be my first guess, but since you've replaced that already, I'd start suspecting the idle actuator. Whether you actually wish to replace it is another story. I don't feel like there's a high percentage it'll fix your problem, so it's a tough call.
When the condition is occurring, this problem should be able to be diagnosed with a scan tool. The scan tool will enable the technician to see data values for pertinent sensors to help determine whether your problem is resulting from a faulty sensor. If you know a shop that is good with these type issues, a professional diagnosis may be your best bet.
