1990 300E EHA stumbling issue EHA
 

I've owned the above vehicle for just over 6 months.
The car has always started, idled and run fine with no issues.
About 1 month ago, I noticed that the EHA had developed a leak.
I purchased a new Bosch unit and installed it with new screws and new o-rings.
After the install, the car stumbled and I had all types of idling and driving issues.
I replaced the new unit with the old leaking unit and once again it ran fine.
My question is, there should be no adjustments after the install of the new unit, correct? It should be a simple replacement. I would have to assume the new unit is bad, correct?
In the mean time, I returned the new unit and awaiting the arrival of another one.
Thanks in advance.