RX 300 Transmittion

[Rexlex]

I have an issue with my gearbox or at least I think that is what the problem is, ok the symptoms are these... when approaching a roundabout for example when I lift off and slow down but don't need to stop completely and then I go back on the gas then I get a thump through the transmission, it's quite abrupt! If I'm really really gentle with the accelerator I can get away reasonably smoothly, I'm quite a smooth driver anyway I don't race the car but this seem extreme and rather annoying because sometimes I forget to be really gentle and so I get the thump again

I've done about 6k since the gearbox oil was changed by Lexus and it still looks pretty clean on the dip stick so I don't think that is the problem, I'm thinking maybe a sensor a speed sensor malfunction or something, anyone else had this issue before??

Thanks guys..    

[sorcerer]

There's nothing wrong with the transmission, it's meant to be like that - sort of.

It's down to the fact that these cars are fly-by-wire. In a 'traditional' system the throttle pedal has a cable attached that runs to the engine - press the throttle pedal and the cable moves the throttle plate. In our cars there is no throttle cable, just a potentiometer. Press the pedal down and a box of electronic wizadry sends a signal to an ECU to open the throttle instead.

Fly-by-wire systems aren't as responsive as a cable system and the electronics lag a bit, so you just have to adjust your driving style to take it into account. You'll get used to it - eventually. I'm coming up to a full year of ownership and it still catches me out!

[ColinBarber]

this isn't really anything to do with a fly by wire throttle, this is the gearbox performing an abrupt gear change - essentially poor management software but I don't think there is anything you can do unless there is a specific problem with your vehicle.

[PCM]

I think I had this too...

Lasted for a journey or two, then it disappeared.

It was a bit disconcerting.

There was nothing I did - it just seemed to right itself.

[ColinBarber]

Certainly worth resetting the ECU as a first step, disconnect the Battery for a minute or pull the ECU fuse(s). This will reset the transmission 'learning' state.