Wa Alaikum Salam,
Had similar problem - RPM fluctuating.
Solved by STP Fuel Treatment.
Car: EFI Cultus (with injectors)
Procedure (also mentioned on STP Fuel bottle): Fill tank, pour the bottle, and by end of tank, issue was resolved.
Only one side concern: After this treatment, the engine oil is suggested to be changed, since the residue is now carried in the Engine Oil (Oil is dirtier now).
Hoping it helps.
Regards.