Hi all!

so my 92 SC400is having some major issue and I cant figure it out

car starts and runs and drives perfect for the first couple miles. Then no matter what gear or speed it seems like the transmission throws itself into 1st gear. (RPM goes to 5k+, loss of power until i slow down to 10mph or so) at this point it will drive but will not change gears and will only go 10-15mph or so.

Heres the tricky part...

If I shut the car off and wait 10 seconds I can turn the car on, put it in drive and it shifts and drives fine for another few miles then does the same thing. (I can repeat this for as long as I need to)

Tried:
1. replacing ECU with a working one from a friends daily driver (same model and ecu part number) = same symptoms
2. No transmission error codes present,
3. CEL shows #13 RPM Signal no2 fail = could this be it?
4. checked fuids = all is fine
5. O/D on and off as well as "L" and "2" gear = same symptoms
6. reverse works at first then stops working when the tanny does its thing but works again after restarting car.


This is driving me insane! at first I thought it was the capacitor leak issue, ruled that out i think. now the CEL #13 code makes me thing it would make sense considering it has to do with my RPM. but then again other people have that code and dont have my symptoms. There is a clear cut recognisable pattern of symtoms to my issue, but no matter how much I search or look I cant find anyone with a resolution or even an idea what it is.....

any help would be greatly appreciated!