jerkiness can be caused by anything mainly..mechanical, fuel or electrical.
1. fuel - maybe insufficent fuel supply or fuel flow not smooth. fuel filters are always recommended replaced every 40,000 km interval. filters for EFI are not as cheap as for carbie mind you. if ur fuel tank is badly contaminated, even the injectors may get clogged.
2. electrical - normal spark plugs are recommended replaced every 20,000km for the most optimum performance. if its due, change it. if not due, spark plugs are not that expensive to change either. a set of NGK BP5ES or BP6ES cost you around RM18-20.
before u change the spark pug cable, try borrowing from another similar wira... and if confirmed problem solved and wanted to change..i suggest u upgrade to thicker cables... maybe 10mm? he he dun worry, this wont affect warranty of ur car.
distributor may give u problem but the chances are very low... nowadays wira use fixed distributor and highly reliable.
3. mechanical - throttle body prob is a common favourite with wiras since long ago. regular servicing always required. if problem cured after servicing but persists again and again..insist on replacement. talk to the manager or call the hotline if necessary. The Star, TV3's karam sing walia and Edisi Siasat are always glad to help. never change the A/T cable's factory setting. once altered, u may never get the standard setting back.
a fren of mine complaint its wira 1.5 auto like no power, Proton Edar mechanic adjusted the cable so that the gear changes at higher rpm say like 3,500rpm instead of 2,800rpm.
power delivery is better but the delayed gearchange got annoying as it refused to change into 3rd gear even at 80km/h sometimes becoz not yet reach high rpm.
my fren cant bear with the noise and higher consumption, asked Proton edar to set back as standard but after few attempts...still cant.
gud luck to you anyway...
p/s wanna change to savvy auto-manual? he he juz kidding....