2002 Subaru Forester Problems after Knock Sensor Replacemen

2002 SUBARU FORESTER
99,100 MILES • 4 CYL • AWD • AUTOMATIC
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KLAWNY
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Check engine light came on this summer and the tech said replace the knock sensor. So I did.

After replacing the knock sensor my city mpg tanked (although highway mpg is still pretty good) and I started getting rough idle and hesitation when it was humid.

Took the car back and they said replace spark plugs and wires.

Rough idle/hesitation cleared up for the most part, but I am still getting lousy city mileage.
Feb 2, 2010 at 6:41 PM
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2CARPRO JACK
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When the knock sensor was bad the computer may have been in a "Limp" or backup mode as far as timing goes, this coupled with a baseline fuel mixture could have created asituation where the engine was leaner than normal, thus got better mileage.Check basics too. tires inflated to proper pressure? Air filter good?
Feb 3, 2010 at 8:08 AM
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KLAWNY
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Thanks for getting back to me.

City mileage was consistently in the 25 -27 mpg from when I bought the car in 2002 until after I replaced the knock sensor this summer - now its closer to 15-17 City.

I dont think tires are an issue as they are less than 25K, get rotated with every oil change and are well inflated.

Any thoughts about the rough idle/stalling on wet and humid days which also only developed after replacing knock sensor?
Feb 3, 2010 at 12:44 PM
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2CARPRO JACK
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No codes in the PCM? Check the fuel pressure regulator, pull the vacuum line off at the fuel rail, if any gas is present, repalce the fuel regulator
Feb 3, 2010 at 5:16 PM