Based on that description, I would not start with the throttle body. Your symptom sounds much more like a transmission-related issue, torque converter issue, or engine load signal problem than an air induction problem. A few observations: The jump from ~2,000 rpm to ~4,000 rpm at 40 mph indicates either: the transmission is unexpectedly downshifting, the transmission is slipping, the torque converter clutch is releasing, or the engine is losing power momentarily and the transmission is compensating. A dirty throttle body typically causes: rough idle, unstable idle speed, hesitation from a stop, poor throttle response. It generally does not cause a repeatable 2,000-rpm increase at a specific road speed. Old transmission fluid from sitting for 2 years is possible, but transmission fluid usually deteriorates more from mileage and heat than simply sitting. At 225,000 miles, however, transmission wear becomes a real consideration. Questions Does the rpm jump occur under: light throttle, moderate throttle, or heavy acceleration? When the rpm jumps, does the vehicle accelerate harder? If yes, it's likely a normal downshift. If no, it's more likely transmission slip. Can they duplicate it with overdrive turned off? Any vibration before the rpm flare? Failed torque converter clutch operation is common on high-mileage U660E transmissions. Things to check first1. Scan for codes with a professional scannerEven if no MIL is on, look for: Current codes Pending codes History codes Pay special attention to: P07xx transmission codes Engine load/airflow codes Misfire history 2. Check transmission fluid conditionThe 2007 ES350 uses the U660E transmission with Toyota WS fluid. Inspect: Color Odor Evidence of contamination If the service history does not show fluid changes, a simple drain-and-fill may be worthwhile. I would avoid a power flush on a 225k-mile transmission with an unknown service history. 3. Watch live data during the eventMonitor: Engine RPM Input speed Output speed TCC lockup status Gear commanded Gear actual This will quickly determine whether the transmission is actually slipping or simply being commanded to shift. My suspicion rankingTorque converter clutch cycling/unlocking Very common around 35-50 mph. Can feel like a surge or flare. Transmission wear/slippage Especially at 225k miles. MAF sensor contamination or engine performance issue Less likely but possible. Throttle body deposits Possible maintenance item, but unlikely to be the root cause of this specific symptom. Simple driveway testDrive at a steady 40 mph on flat ground and watch the tachometer. If RPM briefly rises 1,500-2,000 rpm with little increase in vehicle speed, suspect transmission slip. If RPM rises and the car immediately accelerates harder, it's probably just a commanded downshift. If RPM fluctuates 200-500 rpm repeatedly while maintaining speed, suspect torque converter clutch operation. Given the mileage and the fact that the symptom appears at approximately the same speed each time, my first thought would be torque converter clutch disengagement or internal transmission wear, not a dirty throttle body.

Thank you for the reply and clarification, Ive read 1124 and 1020.

I talked to two auto upholstery shops. These seats have the covers glued to the seat foams so they cannot be easily repaired. So, I am in search for some wine red seat covers for my 2015 IS250 F Sport. Looking for recommendations for custom fit covers.

Circuitry

Hi Steve, Thank you so much for the suggestion. I will definitely buy the KYB ‘coz I heard about good feedbacks on the brand. Thanks again! Ronald