that usually happens when 1 coil gets replaced at a time. truth is they are all the same age and should have all been replaced at once. tough to swallow the price but it happens. i'd be suprised if those are the coils that left the factory when the car was new. generally, 100k is the life of them, give take 10k or so. make sure the plugs are what volvo says are for the car, not some generic thing, and especially platinums. and replace when you're supposed to, 30k i think-might be wrong. 1 more thing-i forget if the coils come with the extensions on them. if not, then replace them also. the extra resistance in the worn plugs and extensions will draw more amperage from the coils and kill them early. good luck, chuck.