Hi,

A '94 Sentra LE here with the 1.6 manual tranny.

Sometimes when I start my car and drive the check engine light flashes randomly while driving. More so when I'm on the gas instead of coasting.

If I turn the car off and restart it's gone.

I have a new O2 sensor, but it was doing it before that.

Car seems to run fine. Any ideas?

Also, when I check the ECU for codes I don't get any codes. I'm checking it manually...not with a tool.

I have that same issue, take it to Auto Zone, they will check it out for free with the ODB handheld. Mine came out to be Multiple Cylinder Misfire. My 2005 Sentra's engine light is on, sometimes blinking when my car really sputters, and I just discovered either a bad head gasket or warped aluminum head, as its leaking water into cylinder 2 & 3. I took out the spark plug and smelled it, smelt like antifreeze. I am going to replace my head gasket this weekend. Hopefully no hitches. This could be your issue as well.