Tuhrak

Hello all,

I have a 2004 Lexus GS300. It has 216.5k miles on it, I got it for 2k USD as it had some bad door damage which was fine as I planned to swap the doors out and paint it anyway.

Over the last 2 months I've owned it, I've finished a plethora of maintenance items - all fluids, all mounts, complete front suspension. Coming to the topic of this post, I also did a transmission fluid drain and fill twice, the most recent one being around 800 miles ago. The fluid became nice and red from the dark brown it was before that. The transmission has always been smooth with no jerks even while I floor it. After the drain and fills it has only become smoother. I used the recommended type of ATF - Toyota Type T-IV.

Today I had a very weird occurrence - I was approaching the freeway merge which was metered, so I was going fairly fast (around 40 mph) and slowed down at the metered merge, but didn't come all the way to a stop, maybe to 10 mph. Then once I got the green light at the merge and accelerated pretty hard, maybe a second later the whole car just jerked whipping my head forward. I looked at the dash immediately, I didn't get any lights - no VSC off, no CELs etc. It all happened very fast so I don't know if it was a bump in the road but I don't think it was as I didn't feel any upward movement that you might notice when you hit a bump. I also hooked up my OBD reader once I reached office and no history of codes/pending codes.

Nothing happened on the way to my office, all gear shifts where super smooth, even while flooring. Acceleration + deceleration was super smooth all the way. Checked ATF which is red and filled perfectly to the top of the hot mark.

The only thing I have done recently to the car recently was replace the two rear tires. The two tires I got don't seem that great (they're OHTSU) and yesterday I had the vehicle skid indicator beep at me on a turn which I didn't have any issues with previously even on high speeds. So I plan to switch them out for what I had originally on the car (Yokohama YK470 GTX).

I understand that this is a tiny sample set which makes it very difficult to draw inferences as to why this happened, but any preliminary ideas on what happened?

1. Will a bad transmission always throw a code?
2. I am wondering if I basically just confused the transmission by braking for a bit and then suddenly accelerated. Like I said the transmission is SUPER smooth and only gotten smoother since my drain and fills.
3. Possible mechanical issue with the transmission requiring rebuild/replacement? Any tests I can do to know better?

DMPesso

It’s not your transmission bro the 2GS can have a delay sometimes if you go from a rolling stop and suddenly mash the gas, especially if you were driving normally before that and not aggressive. It adjusts to your driving habits on the fly. When I drive really hard for at least 5-10 mins the ecu learns and starts adjusting shift patterns accordingly. Reset the ecu see if it happens again. I bet though the issue was your rear tires lost traction for a bit or your rear alignment is off. You should never hear that rear skid beep unless it’s snowing or your driving crazy. Cheap vs good tires make a WORLD of a difference in rear traction and how the car performs and feels. Make sure your rear alignment is 100% or that can definitely cause the delay your describing.

One thing i did notice was after I changed my rear knuckle bushings the hesitation when mashing the gas from a stop went away and it’s a lot more peppy. This is because my rear alignment would constantly go out and the car would struggle for traction in the rear. Turn off your VSC that should help until your rear alignment is 100%. At your mileage the knuckle bushings are definitely worn. Since you already invested in changing the suspension you should do the rear knuckle bushings and front steering rack bushings. Both pretty cheap and easy to do and make a HUGE difference in how the car drives and handles. It was night and day for me

Tuhrak

Thanks for the reply DMPesso, that seems to make sense. I'll probably swap out the front tires too fairly soon. I was fairly sure it wasn't the transmission either as it has been nothing but buttery smooth.

I'll post back if it happens again. it's going to be out of commission for a while as I'm painting it but hope to get it back on the road soon!

DMPesso

yea the rear traction makes a difference. But I just realized did you ever change motor and trans mounts? This will cause the issue you describe more then anything else

CurlyG

+1 check motor and tranny mounts
Motor mount check is easy with 2 people. One person (that you trust) starts the car, holds the brakes while putting it in drive and lightly gassing it. You stand in front, with the hood open, and observe if the engine twerks (rotates) significantly under load. Might be safer to have the driver put it in reverse instead of drive.
I can't think of an easy way to check the tranny mount. It's underneath the car. You could probably lift the car, go underneath with a jack, and jack on the tranny while seeing how the rubber mount responds.

DMPesso

id say don’t even bother checking them if you know they were never replaced most definitely you need to change them. A tell tale sign in the gs however is if you come to a stop and when your idling you feel the car shake a bit. That’s the motor mounts.