[SOLVED : READ BELOW]
Okay, my honda accord hasn't been shifting right for a while now.
But recently, when the car shifts into 2nd, it stalls. I have the error code P0730.
It feels like the downshifting isn't engaging, so it's staying in 3rd, while trying to downshift.
I have reset the TCU
The transmission shifts fine otherwise, so I don't think it's the clutch or anything inside the tranny.
I have replaced all the solenoids and changed the fluid on multiple occasions.
The car also downshifts hard.

Could this be a pressure problem?
Or is it something up with the TCU? Does that need reprogramming/replacement?
I was also thinking the 2nd/3rd clutch pressure switches?

I think it's one of these three problems, but I don't want to spend money on one, just to find it was a different one.
The tranny gears are fine, as well as the clutch plates, according to my mechanic.
Just looking to see if it could be one of these things?

 

It could be, need to verify gears 1-4 have correct pressure.
If the pressure is good, pull the memory fuse and reset the PCM.

Start the engine, warm it up, and then drive the car above 12MPH for over 30 seconds.
If the code is gone you are most likely fine.
If the code reappears, you will need to replace the transmission.
The later 98-02 ATs are not as forgiving and the earlier 90-97 units.

 

How would I do that?(I'm still new to mechanics, and this is my first car)

 

If you don't have an FSM, and a gauge kit, it may just be better to bring the car to a quality transmission shop and see if they can do the test for a nominal fee.

 

Had similar issues on mine a couple years ago. Not to freak you out but i ended up replacing the transmission.

Not saying that is your issue, i had other signs that developed and got worse

 

What exactly have you replaced? I know you said "all the solenoids" but just curious as to the specifics.

Chances are you have a TCU that is receiving inncorrect data from either 1 of its sensors/switches on the transmission OR it is receiving incorrect data from the ECU or one of the engine's sensors.

For example:
If you had a faulty Throttle Position Sensor (TPS), the ECU and TCU may think you are giving the car partial throttle during the time its supposed to shift when you really are not, causing an unnecessary increase in shift pressure.

Also check your vacuum at the intake manifold at idle, vacuum leaks can cause improper Manifold Absolute Pressure Sensor readings. (MAP)

 

UPDATE: I REMOVED THE TCC SOLENOID VALVE 'A'.

It drives fine.
the TCU was damaged and telling that solenoid to shift at the wrong time. Reprogrammed the TCU and removed the solenoid.