Openai/69556a65-a290-8002-a217-eebca2e0b967

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User: 2020 Lexus RX 350 F-Sport with over 47K miles and recently noticed that on occasions when I may need to accelerate and …

2020 Lexus RX 350 F-Sport with over 47K miles and recently noticed that on occasions when I may need to accelerate and it will start to redline and temporarily get stuck and not drop back down to normal rpm’s .

Assistant: That behavior on a 2020 Lexus RX 350 F-Sport 47k miles is not normal and usually points to a transmission or throttle c…

That behavior on a 2020 Lexus RX 350 F-Sport (47k miles) is not normal and usually points to a transmission or throttle control issue, most commonly related to how the 8-speed automatic is managing shifts.

Below are the most likely causes, starting with the most common for this model/year.

Most Likely Causes

1. Transmission Hesitation / Shift Logic Issue (Very Common on RX)

Lexus RX models (2019–2021 especially) are known for:

• Delayed upshifts
• RPMs climbing to redline
• Transmission “holding” a gear too long before finally shifting

This often happens:

• During quick acceleration
• When merging or passing
• After slowing and re-accelerating

📌 Why it happens

• Transmission software struggles to decide which gear to select
• The ECU thinks you still want maximum power
• More noticeable in Sport or Sport+ mode

✅ Fix

• Lexus TSB (software update) often resolves this
• Dealer reflash of the transmission control module

2. Throttle Position Sensor or Electronic Throttle Body Issue

If the car:

• Revves high
• Doesn’t immediately respond when you lift off the gas
• Feels like it’s “stuck” revving

This could be:

• Dirty throttle body
• Faulty throttle position sensor
• Accelerator pedal sensor lag

✅ Fix

• Throttle body cleaning
• Sensor recalibration or replacement (if faulty)

3. Torque Converter Not Locking Properly

A failing or slipping torque converter can cause:

• RPMs to flare upward
• Delayed power transfer
• RPMs staying high even when speed isn’t increasing much

📌 Often intermittent at first, then becomes frequent.

⚠️ More serious if ignored.

4. Transmission Fluid Condition

Even though Lexus markets it as “lifetime fluid”:

• At ~47k miles, fluid can already degrade
• Old fluid can cause erratic shifting and RPM flare

✅ Fix

• Drain-and-fill (NOT a flush)
• Lexus Type WS fluid only

5. Drive Mode Effect

In Sport / Sport+:

• Transmission intentionally holds gears longer
• RPMs stay higher by design

📌 If this happens in Normal or Eco, it’s more concerning.

What You Should Do Next (In Order)

Step 1: Note the Conditions

Tell the dealer:

• Which drive mode (Normal / Sport / Sport+)
• Happens when warm or cold
• Happens during passing / merging
• How long RPMs stay high

Step 2: Ask Dealer to Check for TSB / Software Update

Specifically request:

“Check for transmission ECU or powertrain software updates related to shift hesitation or RPM flare.”

This alone fixes many RX complaints.

Step 3: Request a Transmission Diagnostic

Ask them to check:

• Live shift data
• Torque converter lock-up
• Throttle input vs RPM response

Step 4: Consider Transmission Fluid Service

Even if Lexus says it’s lifetime, many techs recommend:

• Drain & refill at 50–60k miles

🚨 When It’s Urgent

Go to the dealer ASAP if you notice:

• RPMs stay high even after lifting off gas
• Harsh shifts afterward
• Burning smell
• Check engine or transmission warning

Bottom Line

✔ Most likely cause: transmission software or shift logic ✔ Good news: often fixed with a software update ⚠️ Do not ignore — prolonged RPM flare can damage the transmission

If you want, tell me:

• Does it happen in Normal mode?
• How long do RPMs stay high (seconds)?
• Any warning lights?

I can narrow this down further.