the car in question is santro club 2003 EFI
The car holds normal RPM at startup in the morning, as temperature of the engine increases so the RPM, the engine had been producing a noise like ssssssssssssssssssssssssss for 2, 3 months, now the noise vanished, but RPM still high. all the pipes and air suction line checked, no leaks, IDLE CONTROL VALVE replaced with a new and genuine one. but of no use. 3, 4 mechanics just failed to diagnose. finally a mechanic poured some water behind the air filter box and engine sucked the water and stalled, I restarted the engine and he poured little water RPM get lowered for few seconds but engine didn't stall. he concluded that its the loose head bolts or burned head gasket and water is injected in that area. PLEASE SUGGEST WHAT TO DO. The HIGH RPM at idle is on CNG, PETROL, LPG.
one other thing, I removed the IDLE CONTROL VALVE connector the RPM get lowered at cold startup, but same behavior after engine warm up.
It could be the head gasket which is worn out, and sucking air when engine get hot. what experts say.?