this seems to be a common problem on the 97 e420 since it is equiped with the early 722.6 trans. i am having a similar intermitent problem with my 97e420. mine was fine after i turned off the ignition , this seems to reset the computer. eveyone on this froum advised me to do an oil change first and then go from there. i have read about the tcu problem and i suspect that mine is having this problem too.
my question is, where is the tcu located and what do u use to clean it.?
i heard that you should measure the adaption values from the tcu to see if they are at or near max. if they are then your trans is toast and you will need a new one.