| CAUTION | If ECM replacement is instructed in following testing, always ensure ECM harness connector and ground circuit are okay. If either are suspect, repair and repeat testing to confirm ECM malfunction. If ECM is replaced, ECM must be programmed with proper ignition key code for engine immobilizer system. For programming procedures, see COMPUTER RELEARN PROCEDURES - LEXUS article in GENERAL INFORMATION. |
Note. For component location, see appropriate illustration in THEORY & OPERATION article.
Circuit Description
Idle speed is controlled by Electric Throttle Control System (ETCS). ETCS is composed of throttle motor to operate throttle valve to connect throttle motor with throttle valve, throttle position sensor to detect opening angle of throttle valve, accelerator pedal position sensor to detect accelerator pedal position, ECM to control ETCS and one valve type throttle body. DTC is set when idle speed continues to vary greatly from target speed (2 trip detection logic). Possible causes are
- Electric throttle control system.
- Air induction system.
- PCV hose connection.
- Defective ECM.
Diagnostic Aids
Read freeze frame data using hand-held tester or OBD-II scan tool, as freeze frame data records engine conditions when a malfunction is detected. When troubleshooting, it is useful to determine whether vehicle was running or stopped, engine was warmed up or not, air-fuel ratio was lean or rich, etc. at time of malfunction.