1) No issue with the ECU, the engine check light is because the ecu prompts error on
CNG coil although i got mine checked several times so ignore it as long as u r on CNG. but if u start on petrol and stay on n the EC blinks get your petrol sensor checked.
2) u definetly need a tune up, cause mine dose 130 km/hr with minimum efforts on CNG w/o AC. & round 120 with AC. replace your plugs with atleast 2 pin. clean the air filter regularly n get it replaced every 3rd month at max.
3) regular clean up with any good carb- cleaner