My mechanic tells me that a fault code for the upshift delay valve is 90% of the time a problem with the upshift delay valve holding vacum.
It is located on the side of the transmission.
It is a common failure part, and costs abut $250-ish for the part.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".