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99 Legacy Poor MPG Questions


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do you know the maintenance history?

 

If not, I'd do all you list, plus make your Tbelt isn't (over)due...usually every 100K or so.

 

And the CEL is NOT on, correct? But you know the CEL light works? Key ON, Engine OFF?

 

O2 Sensors may be getting weak, but not bad enough to Code..just cause poor MPG.

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Bad Knock sensor will cause poor mileage.  Use an ebay / rock auto cheap one , no need for OE part. Easy to change at small cost.  other than that   New NGK plugs , New NGK spark plug wires.Both cheapest thru rock auto.  New air filter & your fuel filter won't effect mileage but good thing to change out before winter anyway.  Run a can of sea foam thru for your injectors and try to buy ethanol free fuel.

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  • 3 months later...

I have a 2007 Legacy Wagon and my mileage has been dropping over the past year.  26-27 Hwy when it was getting 30+ mpg.  Here's what worked for me.  A $10 can of Mass Airflow Sensor (MAF) cleaner!  10-15 minutes to remove the electrical connector and two screws.  Mine was right near the air filter.  I sprayed the *#$%^ out of it (inside the tube and out) and cleaned it all gently with a Q-Tip.  I just got back from a road trip to Boston (400-500 mi RT) and got a solid 30+MPG again.  My local mileage is still a little off, but it's cold with winter gas so that's not unexpected.  Look up some videos for cleaning yours.  I also had the option of buying a new MAF for $40-$50, but opted for the cleaner first.  I was also a little miffed that Subaru never checked this since I've asked them to check my mileage twice!  Try checking yours.  It's a palce to start that won't break the bank!  Good luck.  CW46k

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It’s hard for Subaru to check poor mileage. They could spend hours checking brakes, codes, O2 signal, vacuum, ignition, leaky injectors and you’ll be billed $300 with no improvement. They’d have a lot of POed customers. And many of those would have an unsolvable non-issue of perceived poor mileage due to job change, life change, driving habit, new house, new hobby, teenagers borrowing car, or some other variable, not actual poor mileage. I’m the odd event they could trust “customer diagnosis” there are too many culprits to easily and effectively rule out. Too many variables, Dealers are in a lose lose situation.

 

While the MAF worked and is fine for free labor DIY it’s a really low percentage guess and dealers would loose money, customer satisfaction for doing it. They’d win your affection but loose it for the next 50 people it wouldn’t help.

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