GS300 mk3 2005 - transmission issue and misfire

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3rd gen GS300 with 98k miles has occasional rough idle on start up as though not running on all cylinders. It clears under load quickly and is very intermittent.  Car has been serviced and had new plugs about 6 months ago.   No fault codes showing up.

It also seems as though the transmission changes to a higher gear too early. i.e to 5th or 6th at around 1200 rpm at modest speed when it feels like it should hold it for longer.  No other problems with the transmission and changes seem smooth enough and works fine on sport/manual shift mode.

Seems more like electrical gremlins than mechanical. 

I have a got a slight blow on the exhaust at the very rear but I cant see that affecting transmission or idle at start up.

Any thoughts or obvious things to check. I am not familiar with the GS300 engine and it baffles me how a transmission fluid can be 'for life' and I cant check it.


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Merry Christmas to all.

Not all trouble codes are displayed on the instrument panel. To eliminate all guess work, I would use the Techstream scanner, the Mongoose or the one used by Lexus.

Intermitent faults usually indicate bad contacts at the connectors. By removing and reconnecting the connectors a good contact is restored.

Never believe that anything in this real world lasts for life! My car's owner's manual states that the gearbox is sealed for life and no maintenance is required. However if you refer to Techdoc ( Lexus repair manual ) it specifies that the gearbox oil should be changed every 72 months or some 60 000 miles, I am not quite sure of the mileage but is around there.

Refer to Techdoc for your car and follow the directives. I would most certainly  change the oil with the recommended oil by the manufacturer and not by any other claimed to be superior, better etc.

I would also disonnect and reconnect all connectors to the gearbox. Also check any damage to the multicore cables pertaning to the gearbox and repair as necessary.

Moisture and water is the cause of all electrical and electronic equippment.

Kindest regards,




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