You description sounds most like a vacuum related problem, as the ECU tries to account for extra air.

I replaced the injector seals on my M103 and the water temp sensor (rear most) at the same time. It made a HUGE difference.

Later on, I replaced all of the small vacuum tubes on the engine and transmission. That made a bit of a difference, too.

The work wasn't that hard, but be careful when disconnecting the fuel lines. Bending one would be bad.