Thanks for the suggestion. I forgot to mention that the car was purchased recently after sitting for over a year. It was very sluggish so I used some injector cleaner, as well as a can of BG44k and also cleaned the intake/throttle body with another BG product. The car started running much better but then this problem appeared.

Someone told me about a valve that prevents fuel from leaking down towards the gas tank when the car is not running. If the valve goes bad, this exact problem would happen because the fuel pump needs a few seconds to pump fuel all the way to the injection system. However, I am not sure if my car even has such a system in place. Any ideas?

The engine is 103.942.