I am reading fault code 2-3-1 in my 93 240. The Bentley says this indicates that the fuel system is compensation for rich or lean air/fuel mixture at cruise. I am not sure what to suspect may be the cause. Consider the following:

Acceleration from stop 90% of the time is normal. However, a small portion of the time, the car will begin to accellerate from the stop the chug like it wants to quit (this is not really good when you have just pulled out in front of another car!). Last night, in the drive through window at the fast food, the car just quit (I struggled but managed to get it restarted).

***the above mentioned troubles with acceleration seemed to begin about 1000 miles ago after the timing belt was replaced at a local shop.

Is this a timing issue from incorrect install? Is this related to the idle adjustment? Could the hissing from under the car near the fuel pump/filter area be related to this in that I need to replace something here(ie occasional fuel starvation)?

Thanks for any assistance.