@ hasan 20
do the following one by one and hope that your problem will be solved, insha Allah..
Use stock size tyre your car tyres diameter should nt increase R14 in any case, if you want good economy and use 30 PSI pressure all the time, not less..
change your fuel filter
see for any leaks specially from pipes to fuel filter and to fuel rail. also tell your mech to check the pressure in fuel rail
Do your car tuning on PETROL from a good tuner.. only do computerized tunning since your car is EFI.
use good quality spark plugs Denso k20 RU or K20 pru-11 or ngk bkr6e11
change the air filter and make sure that the air intake is not sucking air from any where except the air filter inlet.. search this thread on how to check it.. specially visit page 109 and onwards..
Do a throttle body cleaning from good workshop.. Also clean important sensors like MAF sensor and crank shaft sensor
check the condition of coils, if cracked or not passing current then replace them but only if are sure that they are faulty..every mech you go to will invariably point out that your coil are gone.. the best mech should check them on an ohm meter otherwise normal ones shouls at least check them while the car engine is running and see the whether the engine stalls while they take out the coils
if your problem is solved then OK
otherwise also go for petrol tank cleaning and also check the condition of Fuel pump