I have a 97 4Runner with the 6 cylinder. It started idling low and threw a P0505 (Idle control circuit) code. Idle was 500 rpm and frequently would stall out when cold. I've replaced the IAC, checked all hoses, replaced the TPS, cleaned the MAF and still get the P0505 almost immediately after clearing the light. I got a used TB from Ebay. After cleaning this new TB and IAC has the car running at about 750 rpm. All the IACs ohm out correctly per the FSM. There are no other codes beyond the P0505. The power wire is suppling correct voltage to the IAC. At the ECU connection, the RSC and RSO wires have the correct voltage, key on engine off. So, the wiring integrity is confirmed. The valve itself opens and closes when power ang ground are supplied to the terminals on the IAC. Per the FSM, P0505 is supposed to be a two trip code, so the fact that it comes back immediately after clearing is pointing me to an ECU fault.

I'm looking for input before I change out the ECU. I've run through everything the FSM says it could be, but if anyone has run into this before I'd be interested in hearing any potential solutions.

Thanks.

 

Turned out to be the ECU. Pick one up from a junkyard and problem solved.

 

Thanks for posting your solution.