Auto service Reading these days: A faulty or clogged-up air filter could reduce your fuel efficiency and lead to reduced engine power, which is why mechanics recommend getting it replaced every 12 months or 12,000 miles, whichever comes first. If you think your filter needs checking or replacing, simply locate the filter (usually in a black box under the bonnet) and remove it, making note of how it fits before you insert the replacement and fasten the box back shut. More of a replacement than a check, but spark plugs are integral to the running of your engine – one …