Hi NN820, Welcome to Autolanka forum.
As MINIACE mentioned, tune up was not applied correct. Other than that .......
Is your car is EFI ? If its please check the throttle body. sometimes they have decrease the engine speed as very low RMP range (standard range should be 750 RMP).
Is there any problem, after when you switch on the AC? If its please clean & adjust the AC idle-up sensor (i think its in the throttle body) from the qualified technician. Because this has arised to my Mazda Familia also (not engine in idle mode, its running with AC only). Some technicians said the problem is in the ECU system and AC sensor.
From Pa*la Auto guys has clean this sensor & checked the ECU system. After that issue has fixed. But after one or two weeks again it has arised. Still could'nt fix this my machine also
Will better to find a good place to do this...