I've gotten a lot of good information from this group so I feel
obligated to post a solution to a problem I was having.
1995 S320 would start good cold in the morning or after cooling off
2-3 hours after running. The car required at least 2 extended
attempts to start anytime after 5 minutes running or more.
First it was suspected that one or more injectors were leaking down
into the cylinders creating a pool of fuel that would make it
difficult to start and possibly this pool of fuel would evaporate
several hours later and the car would start fine. Next, the O2 sensor
was changed thinking it was sending a mesage to the brain that it
needed to run full rich.
Neither of the above scenarios was the case. Upon pulling the vacuum
line on the fuel pressure regulator, I saw fuel drip out of the vacuum
line! Appears that the diaphram failed. Changed the regulator and it
now starts perfectly, first time, under all conditions.
Hope that helps someone,