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I picked her up today and I do not know the maintenance history. she has 160k miles and runs awesome. I wanted the HX as it had the highest mpg than any other civic. Since this is my DD I need it stay reliable and get the best gas mileage it can.

What preventive maintenance should I do? Besides changing oil and filter right when I get it.

Gas mileage. I was gonna run some seafoam through it, change the filter and plugs but what else will help on the mpg? Intake, exhaust, chip ?

Thanks guys

 
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Hello and congrats,

in all honesty if you want the most MPG leave it stock, adding an intake may decrease your MPG as well as an exhaust due to the fact your ECU will dump more fuel to keep up with the increased amount of air, the engine will work harder to due the fact an exhaust will be less restrictive and the motor will not the the necessary back pressure.

Sea foaming is hit and miss, if you sea foam a civic yes you can clean the motor but then you might developed an issue burning oil since were the gunk built up over time would be gone, also sea foaming is not the best for your catalytic converter as all the carbon in the motor will now go to your cat and could plug it.

I would definitely do oil change and filter, maybe fuel injector cleaner, new fuel filter, and plugs and wires, maybe even a rotor and cap. I would check your grounds and your front end such as bail joints (common on the civics)

I'm not trying to scare im just saying what could happen.

 
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The HX I believe has 2 catalytic converters because of the wonderful lean burn engine. I wouldn't use seafoam it. Slowly pour in some hot water through the brake booster suction line at high idle with engine being hot to clean out the carbon. Be careful of stressing the rods.
1 common thing I've seen on the forums are o2 sensor issues with the more complex emissions systems of the HX, and with the automatic transmission which you don't have, Honda's CVTs weren't reliable back then. So hopefully the O2s won't bother you any time soon.

MPG: You can increase your MPG by buying a scangauge to figure out the air:fuel ratios to know when the engine is leaning out so you know when pressing on the gas will kick it out of lean burn. I've heard on a manual 1st gen Insight you can do a throttle position sensor trick to keep it in lean-burn more, not sure if applicable to a Civic. (http://autospeed.com/A_112735/cms/article.html)