K&N Cold Air Intake Kit: Increase Acceleration & Engine Growl, Guaranteed to Increase Horsepower up to 12HP: Compatible with 2.0L, L4, 2005 FORD (Focus), 57-2559

The hardest thing about this kit was disassembling the stock intake system. Even then, all it was was just accessing bolts and other fasteners. The performance is excellent and was as expected. I love intake noise and this definitely has it.The negative:My ECU is throwing a too lean on bank 1 code. This is due to the improper sizing if the intake tube that the mass air flow (MAF) sits in. The MAF for my 2005 ford focus zx4 is programmed to detect air in a specifically sized intake tube. Since this tube is larger the MAF is unable to read accurately the air flowing through the tube.

I've read many mixed reviews about this particular cold air intake from K&N. From my personal experience, I would say, overall, it's worth the money--barely.Pros:Increased throttle soundSmall acceleration increaseMPG increase (up 5-10 more MPG/ tank avg)'Kind of' appealing look (looks better than factory system)Cheaper than OEM partCons:Relatively difficult to install, I went ahead and had my mechanic do it, took roughly an hour, cost me an additional $66 ('05 Ford Focus)Not very 'sporty' lookingFilter is hard to reach for future cleaningOverall, I would recommend this to someone looking for an OEM replacement filter, looking to gain a small power and MPG boost, and or trying to add a bit of a throaty sound to your engine; anything other than that and you're wasting your money. I will note that it is IMPERATIVE that the MASS AIR SENSOR be put into this intake facing the 'fresh air' side of the intake. Installing the mass air sensor backwards will create a load of issues (rough idle, engine dying, extremely poor acceleration, check engine light, etc), trust me I know.

There seems to have been gas mileage lost by this addition, not gained as I suspected with a free flowing unit. Installation caused the check engine light to come on, I think it flows more air than the MAS can keep up with. In hindsight I should have just left the stock unit on there and spent my money on suspension upgrades.

This item is freeking amazing! The crappy stock system lasted 100k miles but costs nearly $400 to replace. I instead tried the Steeda intake system. Didn't notice any real difference from the stock system other then it looked better. The Steeda cover is annoying every time you try to replace a light bulb on that side of the car. My focus reached 175k and the milage had dropped to 29-30ish. I gave it a good tune up and had no increase in power or mileage. I then decided to switch the coils because that really helped my jeep that has 224k on it. I got the coils through amazon, a set of 4 for $40ish. They were terrible. My mileage dropped to 27-28, my car struggled to start, bad deal all around. I will replace the coils soon. On a whim I decided to try replacing the intake system again with this one from K&N. Took the rest of the stock system out, what a piece of junk, and put this one in. Immediate results! The car fired right up. Felt strong again milage jumped right back up to 30-31. The system sounds good and was simple to install as it comes with great instructions with lots of pictures (I will admit it, I like pictures with instructions). Plus the best part is I won't cut my hands replacing light bulbs anymore! If you have need to replace your stock system then rip that piece of garbage out and get this you will love it!

Engine will run lean … then in a week or so it won’t even turn on … sucking to much air …

This is a 1/3 the cost of OEM. These factory (lifetime/30K mileage/ 36 month) contained filter units just did not make sense and at 450.00. the cost was just not justifiable.I purchased these filter units for a 2004 and now a 2005 Ford Focus. Instant mileage improvement of 12%.Clean twice a year and be wary of the lubricant. It will give false sense failures. Clean the sock and blow up the filter and you are good to go.

Gave my car a check engine light. Other then that looks nice sounds nice.

I bought this for my focus because it had the lifetime air filter and a factory replacement was going to be more than this. I did gain a little bit of power not sure about getting any better mpg though. The worse part of the install is getting all the factory parts out of the way. I guess my only grip is this caused my engine light to come on. Oh well no biggie for me for the money i feel like this is a good upgrade especially for people with the lifetime air filter.