My furnace fires up and after a couple of minutes the flame goes out but the blower keeps running for awhile, I cleaned the heat sensor and re-installed and the flame stayed on longer but after about 4 minutes it went out again but the blower kept working, does the heat sensor need replacing.

If the is flame sensor is bad you would only get flames for a few second's.Sound's like maybe it's going off on high-limit. Make sure the filter is clean.

Does it show any codes? Possible roll out although that is usually quicker. Does it have adjustable high limit?