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Diagnosis & Repair

WARNING: This page is about a different car, the 1995 Lexus LS 400. However, it is still accessible from the selected car via links, so may be relevant.
  1. Disconnect IAC valve connector. Measure resistance between terminals No. 4 and 5, No. 5 and 6, No. 1 and 2 and between terminals No. 2 and 3 at IAC valve harness connector. See Figure. If each reading is 10-30 ohms, go to next step. If any reading is not 10-30 ohms, replace IAC valve.
  2. Remove IAC valve. Connect a jumper wire between terminals No. 2 and 5 at IAC valve. Using another jumper wire, connect one end of jumper to negative battery terminal. Touch remaining end of jumper to IAC valve terminals No. 4, 1, 6 and 3, in that order. IAC valve should move to closed position.
  3. Ensure jumper is still connected between terminals No. 2 and 5. Using another jumper wire, connect one end of jumper to negative battery terminal. Touch remaining end of jumper to IAC valve terminals No. 3, 6, 1 and 4, in that order. IAC valve should move to open position.
  4. If IAC valve does not operate as specified, replace IAC valve. If IAC valve operates as specified, check for open or short circuit in wiring harness between main relay, IAC valve and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary.
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