Volvo: Self Diagnostic Code 2-3-1, mass air flow meter, air intake hose

Question
I have a 1989 Volvo 240 DL.  It starts rough and runs rough at low speed. It feels like it going to stall at any moment when it stands, like at red light.  When is gets going if runs OK, especially at high speed.  Once in a while it jerks, like its loosing power.  This car comes with the self diagnostic box.  I checked the code and it say 2-3-1.  According to Hynes auto book, it means that the system is compensating for rich or lean fuel mixture at cruise.  How do I fix it?

Answer
Christine,
Yes the code you have is what we call a fuel trim code. The control unit can not adjust the fuel mixture properly. So why? Well fuel pressure not correct, fuel pressure regulator leaking, vacuum leaks, even a bad mass air flow meter, broken air intake hose, clogged injectors, blocked fuel filter, I have even seen where a feed pump in the tank was not working and at times was starving for fuel.