88 300E Sputtering Problem

[moohampshire]

Please excuse the charaterization of what it is doing. The car will run great for about 15 to 20 minutes. From a stand still will run fine. After about 15 to 20 minutes it will sputter off the line where you have to play with the gas peddle to get it going and even flor it to get off the line. I have just replaced the fuel filter as I thought that might have been the problem. The one I took out was original and had water and ugly stuff coming out of it. Just put in a new battery in last week because other one was 6 yrs old and failing. Pulled the ovp behind the battery and the fuse was good but changed it anyway. The check engine light is on. How can I check why it is on to start with and what might me my problem. As usual this site is great for help and would expect nothing more.

Thank you for your help in advance.