Air Filter woes - Martin Wall
OK - I decided to get my car serviced on the cheap and got a Kwik Fit oil change - which was fine - and bought an air filter out of Halfords. Alas the air filter was about 2mm too big (Halfords patter part just the wrong size) so I had to put the old one back and the air filter 'box' in my old Japanese hatch needed a fair bit of pushing and shoving to get the filter back in. Since then I've noticed a roar when accelerating - quite pronounced at speed and the car is more hesitant to gain speed.

I guess too much air is getting in somewhere - yes? How can I find out - short of taking it to a dealer instead of being a cheapskate!
Air Filter woes - Dynamic Dave
Are you quite sure you've refitted the old air filter correctly? Sounds to me as if you've not screwed/clipped the airfilter housing back together properly.
Air Filter woes - Onetap
Ventilation air filters have a useful secondary role in that they act as inlet silencers/sound attenuators, reducing the fan noise. If there?s a break in your filter housing or hoses, this may account for the increased engine noise/roar.

If so, then perhaps the weakened mixture would account for the loss of performance; I?m not sure on this, any tuning enthusiast care to advise?