Ensure engine is at normal operating temperature. Ensure idle speed is 650-750 RPM. Ensure transmission is in Neutral. Turn A/C off. Connect Fused Jumper Wire (09843-18020) between terminals TE1 and E1 of DLC No. 1. See Fig 1. On ES300, DLC No. 1 is located on front of air intake chamber. On RX300, DLC No. 1 is located on left side of engine compartment, behind fuse box.
On all models, engine speed should increase to about 1000 RPM for about 5 seconds then return to idle (650-750 RPM). If engine speed is as specified, go to AIR ASSIST SYSTEM . If engine speed is not as specified, disconnect jumper wire from DLC No. 1. Check IAC valve operation. Replace IAC valve as necessary. See IAC VALVE OPERATION . If IAC valve is okay, check for open or short in IAC valve wiring. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair wiring as necessary. If wiring is okay, replace ECM.

Fig 1: Identifying Data link Connector (DLC) No. 1 Connector Terminals

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

System Operation