Check engine light flashes

My 2000 Volvo v40's check engine light flashes, and it stall a bit while on the highway at about 50 mph. Once I let my foot of the gas peddle the flashing check engine light turns off, and the vehicle stops stalling. I recently gave it a tune up because the check engine had come on while in parking. Any idea of what could be going on. I want to have an idea before I take it back to the mechanic.