Yea, my car used to do the exact same thing about a year and a half ago... I was working on the car and noticed it was unplugged, didn't know why, so I plugged it back in. Once I did that, the thing idled sky high... I Replaced the IAC (sucked) and reassembled it the throttle body. It still had the high idle... We looked around, it seemed that whenever the previous owner got the IAC to close, they unplugged it, then used the adjustment on the cruise control cable to hold the throttle plates open just a crack. Once I readjusted it, the car was good again. I really did not enjoy replacing that IAC. I took the nuts off the rear transmission mount and jacked the rear of the trans up to tilt the engine forward a little. Then I removed the TB and took it out without removing the cowl.