Honda: Honda Civic DX 1991, honda civic dx, haynes manual

Question
I have a japanese rebuilt D15 Engine. After 20minutes driving my engine light comes on. it is also very gut less below 3000 RPM and surges back forth sometimes slightly loosing power. Otherwise it runs very smoothly. I only get about 300 KM per tank however. (180 Miles) the plugs cap roter and wires are about 1.5 Years old.

can you tell me why I have low power at low RPM. Why the Engine light comes on, and why I get such bad gas milage?

What can I do?  

Answer
First check the code look in a chilton or haynes manual on how to check it.Perhaps the two symtoms are ralated.These types of problems are difficult at best to diagnose without seeing and hearing the car.If I had to guess I would say the timing is off maybe even the timing belt.If the belt is retarded one tooth the car will run poorly at low rpm and steadily get better with higher rpm.Also check the ignition timing.