Hi, I have a problem with my 93 Saturn SC2. When the engine is cold, it runs fine, but once it gets warmed up, when you run a steady speed, the engine surges. A check-engine light will come on and then all returns to normal.

I checked the check engine code and it calls a code 44. I replaced the O2 sensor and still have the problem. Black soot comes out of the exhaust as well. This engine was just completely rebuilt.

Any help? Thanks

My Haynes manual lists a code 44 as-possible defective master enable relay or its circuit.