4efe sparkplugs

[Andy 1958]

1998 corolla with 4efe 1332cc engine, twin earth electrode sparkplugs are specified, but can single electrode or Iridium plugs be used, or do they cause running problems. 

[TonyHSD]

No, 

you won’t have problems using one electrode plugs, in many ways these are the ultimate plugs. All you need to do is to buy the exact replacement ones, to match the oem numbers. Buy quality plugs from known vendors because these parts and particularly original plugs from non official dealer often comes as fake and those are the worst. 
Good luck