How do I fix my 03 2.0se focus wagon?

I drive my car all day making several stops. Then at one point I start my car but,after it starts it will not stay running it just dies. Restart dies.repeat. Restart stays running as long as you give it gas. Dies, restart hold gas peddle down runs fine foot off of gas dies.Restart hold gas take off drive down road few miles runs fine. drive 1,000miles later does it again. 03 ford focus wagon 2.0 se