Ralt+Home starts the autostart process for the left engine, rctrl+Home starts the right engine. Once you start the process you don't need to keep the keys held down to finish the startu process.
If your engines aren't responding to the throttles after startup, you have an axis assignment problem - there's no key, switch, or process needed to "engage" the throttles.
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Shoot to Kill.
Play to Have Fun.