This seems to be a very common fault code on 93-95 W124's with the M104 engine.
The upshift delay valve is on the firewall behind the master cylinder. It has a black electrical wire and a green vacuum line going to it that connects to the transmission.
The part is cheap, less than $30, if I remember correctly.
You can replace the part and make sure the vacuum line isn't plugged up.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".