On my 1986 240 (LH 2.2), the main fuel pump runs whenever the ignition switch is in the on position. It abruptly began doing this. I can start the engine if I immediately move the key from the off position to the crank position, and the engine idles. However, any delay (with the key in the on position but the engine not running) will cause the engine to flood, and after a few minutes in this state, gas is present where the rubber intake air duct connects to the intake manifold.

The following parts have been replaced recently: main fuel pump, fuel pressure regulator, and fuel relay.