check engine light flashing in 2002 Rodeo

2002 Isuzu Rodeo. The "check engine" light has come on. It flashes when the gas pedal is applied or when down-shifting. It stays on (without flashing) when the vehicle is at a complete stop, the brake is applied, or the clutch is in. Occasionally, there is a loss of power in first gear initially. Any ideas what the cause might be?

Thank you.