Same problem i had with Landirenzo CNG (Not fitted by Company). What you might have to do is:
1.Check Coils with Ampere Meter from Some one and refer to Suzuki Liana Manual for voltages. Also check shortage in any coil wires.
2.Get that Shim trimmed from any Engineering Mechanical Works shop in Saddar , specially Mitto Hatta Bazzar, Riaz & Sons Engineering. They will solve your problem even if it is not repairable . They did mine.
- Install Platinum NGK Plugs and get the gap adjusted by mechanic for better performance. (Gap adjustment is must , most of the mechanic says no need in platinum plugs. but it is the most important.)
Finally, I believe if you will go for 2nd point shims adjustment , your mileage ,pick and all problems will be solved. coz this is the main reason i believe i had.
Please post your feedback if you will apply all of the above suggestions on your own risk .