When the A/C is switched on the engine ecu increases the idle speed by a few hundred rpm to make sure the engine does not stall and keep a "smooth" idle. This is normal.
Also, the A/C system can demand some 10bhp or so during its operation - which is why some people will switch off the A/C when doing an overtake for example.
So, if you want the power back ...
As stated in the manual the recommended grade is 20W40 for that model and year.
Maruti Suzuki recommend various manufacturers oils - and offer co-branded versions under the following part numbers:
Shell Helix: 99999M20W40-SHL
Total Quartz: 99999M20W40-TTL
Any of those will do the job.