New answers tagged troubleshooting
I doubt it would be the ECU. Those are typically all-or-nothing. Sounds more like a bad wire or electrical connection. Test the wiring harness to the injector with an analog volt meter. Put one meter lead to ground and the other on an injector lead while the motor is idling: If the needle doesn't swing then try the other injector lead (if there are two, ...
Welcome to Stack Exchange :) Poor acceleration is sometimes caused by dirty spark plugs or clogged air filters. Keep in mind that the spark plugs are probably more difficult to reach on a 99 Subaru than most other cars since the Subaru has a boxer engine. But, if you feel up to it, you could try replacing the spark plugs ( and/or air filter if necessary ) ...
I had the same problem with my Katana 600. Ran some Seafoam through it and it got better, presumably cleaned up any deposits from gas sitting in the carbs too long.
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