MBWorld.org Forums - 2002 A160 AUTO

Hello, everyone. Very nice forum with helpful information overall indeed. I am new (just registered) and I would like to share with you all my problem. Almost 2 weeks ago (on April 4th, 2018) I bought the A160 year 2002 W168 - long - auto transmission with just 44000 km and I paid at least 2000euro more than "street price" because of the as new condition. Before buying it, the car was checked by an experienced MB mechanic (worked for years at an authorized dealer now he runs his own shop.) and he assured me that the car is almost "new" and he recommended to buy it without hesitation.
The car run very well for a week (did about 100km) and then I decided to ask from a specialized and high professional shop to clean it inside (Biological cleaning) and "wash" the engine as well. Despite the fact that the condition of the engine and the inside cabin was in as new good condition (just dust over the years). The car had been used few times over the years that is why after 16 years has only 44.000 km. After I pick up the car from the cleaning shop I drove for about 50 km and just before I was ready to park in my garage I heard a funny sound from the engine (lasted 1 second) the car lost power and the following yellow lights came on: Engine / BAS / ESP. Switched off the engine and was able to turn the engine on again after 2 - 3 minutes. Then I parked the car. The car was not displaying on the dashboard which gear the car is in (ie doesn't display-P or R or 1,2,3,4 or D)
Does not show an "F" either. Just nothing displayed there.
Also to mention when engaging in drive (D) or reverse (R) the transmission is very harsh and the engagement happens with quite a severe thump.
Drove the car to the mechanic the next day (speed could not go higher than 50km). He plugged the star diagnostics in and he told me that there are many (2-3 pages) "communication errors" did not take any print outs.
We agreed with the mechanic not to do anything and to do reset. Left the car and the mechanic drove it for about 20km distance - problem. Picked up the car the next day drove it and all "symptoms" were gone. No "yellow lights" on the board, very smooth (as should be) engaging in drive or reverse (R) or Drive (D). Unfortunately, after driving about 40km the same yellow lights came on (Engine / BAS / ESP) the car lost power, and all above "symptoms" came back including the transmission was very harsh and when engaging in drive (D) or reverse (R) the engagement happens with quite a severe thump.
The mechanic plugged the star diagnostics in and he told me that "the same" (2-3 pages) "communication errors" came up. Did not take any print outs this time either.

The mechanic gave up and now he recommends getting the car to a specialized "computer memory expert" to check it since he has additional "tools" and should come up with what must be done.

The reason for all above could be because someone professionally washed the engine of my car? He did a light wash (not much water used he said) or I am just unlucky and bought a problematic car?
Called the previous (for 16 years) owner and she assured me that she never had such a problem before. Both myself and my wife like this car and we have it for just less than 3 weeks now. You can imagine how we both feel. Please for your help and assistance. Thank you in advance!