Yamaha EF1000iS Service Manual page 92

With no load, engine speed does not increase when economy control switch is
set to "OFF".
With no load, engine speed does not decrease when economy control switch is
set to "ON".
With load, engine speed does not increase when economy control switch is set to
"ON".
Check AC output.
GOOD
Rotate the shaft of the throttle control motor.
GOOD
Check economy switch.
GOOD
Check the connections of the wire harness connectors
and couplers, and the wires for an open circuit or short
circuit.
GOOD
Replace the control motor.
THROTTLE CONTROL SYSTEM
NO GOOD
NO GOOD
NO GOOD
NO GOOD
6-7
TRBL
Refer to "GENERATOR SYSTEM" in
CHAPTER 5.
Replace the throttle control motor.
Replace the economy switch.
Correct or replace.