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1998 LS400, 275K mileage. Car stalled out at 3 different stoplights and then immediately would crank back up. No Check Engine or any warning besides pretty low idle. At a different stoplight while waiting, engine revved sudenly to 5K RPM so I put it in neutral and shut off engine. Cranked back up fine. No codes, no check engine, etc. Mechanic replaced Mass Airflow Sensor and didn't believe fuel pump was the culprit. Get car back and drive for 2 days with no issue and then this morning while at a stoplight waiting engine gets over 6000rpm before I shut the car off. Attempted a restart and engine immediately went to 6000rpms. Let car sit for a few minutes, cranked it back up and had normal rpm so drove home. Ideas? Obviously I will have the car towed again to mechanic because this issue is extremely dangerous but maybe he needs some guidance on exactly what is going on. Mechanic is very competent but there are no codes to diagnose and he drove the car over a two day period and never had any issue so.......
Note that the 1998+ LS 400 are drive by wire, meaning the throttle body is controlled electronically. Maybe that unit needs to be cleaned or isn't functioning properly. Has the ECU ever been checked?
If your mechanic took off an OEM MAF and replaced it with aftermarket, the OEM unit should be reinstalled in my opinion
Note that the 1998+ LS 400 are drive by wire, meaning the throttle body is controlled electronically. Maybe that unit needs to be cleaned or isn't functioning properly. Has the ECU ever been checked?
If your mechanic took off an OEM MAF and replaced it with aftermarket, the OEM unit should be reinstalled in my opinion
ECU was last checked about 30K miles ago when timing belt/water pump were replaced by another mechanic who specializes in ECU's on high end imports. I may have to check with him on this.
Are your floor mats clipped in properly and not getting stuck pushing the throttle down?
Yes they're clipped on and OK. It happened only at stoplights after I'd been waiting about a minute for the light to change and my right foot resting on the brake. I only use one foot for driving too The sudden surge hasn't happened while moving, only at a dead stop.
When was the last time when engine mounts were replaced? Aged engine mounts cause some vibration when idling and this causes the TPPS ( Throttle Pedal Position Sensor ) some mechanical stress and this affects the output voltages. I'd simply monitor the output voltages of the TPPS first. The voltages of Pin #1 and #2 are deeply related.
Engine revs 5-6K RPMS at stoplight
The sudden surge hasn't happened while moving, only at a dead stop.
