Following up on a real good possibility suggested by dpetryx,

You can check this:

Disconnect output lines to all the fuel injectors from the fuel distributor.

Bridge socket terminals corresponding to terminals 30 and 87 of the fuel pump relay. Engine is off, but ignition swicth is on to get the fuel pump going.

When the air sensor plate is on the top, no fuel should flow from any of the fuel distributor outputs. Then when you gradually press the plate, equal amount of fuel should flow from all the outputs. If this does not happen, need a fuel distributor replacement.

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Saumil S. Patel