My father owns a Civic 95 and runs it mostly on CNG. It has a problem that when the rpms are set at about 700 for CNG and the A/C is switched on they drop to 200-300 and nearly stall the engine. However, at times the rpms go to about 1200 which is normal, I think, for taking the load of the A/C. However, this drop in rpms also occurs even if the A/C is not on and after sometime the engine returns to normal (700 rpms). As a result my father had the rpms permanently set at about 1400 to cater for A/C load but this results in poor fuel economy. What could be the reason? I would be grateful if anyone could diagnose the fault. Thanks.