hey i could not help but try to help coz for the past 6 months i have been having the same problem with my MB w124 260e 1987, it can be a real bore coz it goes n comes back and i mine the same way like yours mine has also been asleep for almost 2 years. i think you should change your 02 sensor to a new one and your problem will go away. if you have checked the idel sensor and it seems to be ok then am sure it is the 02 sensor sending a bad reading when i changed mine the problem went away.