Looking for what might be the problem before I tear into my transmission looking for god knows what.

So car is currently at 114k.
Oil change was done little over a month ago.
Belt was replaced with oil change.
Spark plugs are good.
No codes.

I have an automatic with the steptronic.

I haven't checked anything else.

Everything is fine when the car is cool. Once everything warms up the issue shows it's ugly head.
When accelerating from stopped the car hesitates at first. It'll rev up and move slow. If I let up and let the rpms drop it'll slam into the next gear and then all is well. If I don't let up and keep trying to accelerate it'll still slam.
Going from 30mph to stopping is just as bad. Right around 20mph it'll slam down.
If I'm in the steptronic mode going from 3rd to 2nd it slams. Going from 1st to 2nd it slams.
And when I mean slams it feels like I'm being rear ended. It's forceful jerking and a loud bang.
Only every once in a while will the asc dash light flash. Not every time.
Nothing else shows up.

Anyone have any ideas what this could be?

 

Considering the mileage, you're due for ATF flush and filter change. worst case scenario, the valve body is going bad and if this continues, you might loose the transmission as the clutch packs are getting hammered with each slam.

 

I agree with MiniToBe. Sounds like your transmission valve body is worn out. The reason it is fine when it is cold is that the fluid is thicker and can't seep through the worn valve bores. Once it heats up and thins out, it is able to get past the valves and retain pressure on things like the torque converter clutch and other items. Definitely try changing the fluid first but be prepared to have to swap the valve body.

 

I agree with the guys above. Get a trans fluid flush first.


Motul Gear300 75w90 Synthetic, is excellent trans fluid. You can by it by the bottle on Amazon.

 

In this instance, that is not the correct fluid. Since the OP has an automatic transmission, a JWS 3309 compatible fluid is needed. There are multiple threads on fluids that people recommend, Toyota T-IV, Royal Purple MaxATF, among others.

 

Thanks everyone.
Is there a way to inspect or test the valve body for failure? Or is this issue the only way to for sure know?

 

Not really. The first thing is to change the fluid and change it multiple times to try and get as much old fluid out as you can.


Here is an older thread that can be of help in getting the fluid changed.


https://www.northamericanmotoring.co...ed-at-80k.html

 

The valve body can be tested for failure but I doubt any DIY home mechanic is set up to do the testing.

3 part series
https://www.sonnax.com/vacuum_testing

Testing guide specific to Aisin trans:
https://www.sonnax.com/tech_resource...uum-test-guide