2002 Subaru Forester Problems after Knock Sensor Replacemen

KLAWNY

MEMBER
2002 SUBARU FORESTER
4 CYL
AWD
AUTOMATIC
99,100 MILES

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.

3 Replies

2CARPRO JACK

MECHANIC
11,533 POSTS

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?

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Wednesday, February 3rd, 2010 AT 8:08 AM

KLAWNY

MEMBER
2 POSTS

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?

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Wednesday, February 3rd, 2010 AT 12:44 PM

2CARPRO JACK