I have a 2006 Is430 CL that had been giving me the infamous rough downshifts at low speeds and occasionally rough up shifts.

I read on a many forums that it was the ECU that was giving me my problem so I had sent my ECU over to Josh at Relentless Motorsports for repair.

I've had it back for about a month now and it has definitely helped my problem a lot but I still get the rough shifts occasionally.

I was driving on the interstate yesterday and everything had been driving fine, I took my exit and approached a red light, as soon as the car came to a stop my check engine light came on and the car didn't go when I hit the gas again. I turned off and on the car again and check engine light went away and the car drove normally.

That was the first time l've experienced that and I'm curious as to if it's my ECU or my transmission at this point? I replaced my transmission fluid prior to sending my ECU to Josh and that did nothing.

I really don't want to sell it if anyone has any suggestions I would really appreciate it.

 

Start with the basics-
When you replaced the fluid did you use Toyota WS?
How much fluid was replaced, all or just the contents of the pan?

 

I’m not 100% positive I had it done at a shop.

 

Find out what code got stored when the check engine light came on and see if it is the same as what is listed on the invoice for the fluid change (P0712).

P0712 Lexus Code - Transmission Fluid Temperature Sensor 'A' Low Input. If it is, you need to address why that code keeps coming back...

 

My LS has 246K miles...
From my experience over 3 yrs and 49k miles, I have discovered two things.
1) Replacing Mass air flow sensor helped with "driveability" issues like throttle input and response. No more odd downshifts, nor weird rpm fluctuation. In other words instant smooth responses via the throttle.
2) Using Chevron, Shell, 91 octane gas helps car's response and performance. Once I quit using CostCo gas, my car has run much smoother, with no issues.
I realize these might not be directly related to your potential transmission issues, however they are responsive solutions to driveability issues for the LS430s.

 

That’s interesting, as I thought costco sold Top Tier gas.

I have used Sams Club premium for years, no issues. No Costco here…

 

Unless the service was done at Toyota or Lexus, they probably didnt use the correct type of fluid (WS). this car (w/ the 6 speed trans) is very specific about the type of fluid needed in the transmission

 

$69.00 does not seem correct for WS fluid and filters. Should be a lot more. Replacing the fluid in the six speed transmission is very specific.