1999 Mercedes Benz CLK320 Intermitent problem

Sounds like your transmission is hanging in gears. This can be due to a number of things but most noteably and easiest to repair could be a severly clogged transmission filter. This can also be due to a failing transmission valve body. I would definately recommend taking this in to be properly diagnosed before any damage occurs to the trans.

I change the ECU and the plate in the valve body. It works good now but once in a while mit goes to neutral by itself. I turn it off and on and the problem goes away. When is cold in the morning sometimes it does not release the gear and I have to go to the on/off procedure. I am sure it is an electrical problem, but what electric component might be ??

Although i cannot say I have seen this, I would suspect a neutral safety switch causing the kickdown into nuetral. Aside from this, it you have replaced the valve body and the transmission shift points were relearned properly you may have an internal issue with the pressure plates not holding in the trans. Do you notice it being more one gear than another. For instance do you notice this happening more in the shift from 1-2 or 2-3 or 3-4 or 4-5. Does it happen on upshifts or downshifts or both. Like I said if you feel this is electrical I would go after the neutral safety switch.