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P0303 - next step?

5 messages,  Last post on Dec 03, 2012 at 3:25 PM

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What is this discussion about? Subaru Forester, Wagon

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#1 of 5 P0303 - next step? by crawfe1

Dec 03, 2012 (8:41 am)

Hi. 2006 Forester 160K miles. All of a sudden, very rough idle, good at higher speed. Blinking CC; CEL on or blink. Initial diag: P0303, compression <<100 on #3. I have to use a new dealer so no track record for trust. Does the low compression rule out simple problem like wire, plug, coil, etc.? What would you check next? New to Subaru; Thanks!

#2 of 5 Re: P0303 - next step? [crawfe1] by ateixeira

Dec 03, 2012 (10:23 am)

Replying to: crawfe1 (Dec 03, 2012 8:41 am)
Gotta be a head gasket I'd think...

#3 of 5 Re: P0303 - next step? [crawfe1] by xwesx

Dec 03, 2012 (11:42 am)

Replying to: crawfe1 (Dec 03, 2012 8:41 am)
Low compression could be many things, including a sticking valve, timing, rings, head gasket, etc. It probably isn't a "simple problem" like the wire or plug. More testing is needed to pinpoint the problem, starting with a leakdown test.

#4 of 5 Re: P0303 - next step? [xwesx] by crawfe1

Dec 03, 2012 (1:25 pm)

Replying to: xwesx (Dec 03, 2012 11:42 am)
Thanks. I'm curious why it's better at driving speeds?

#5 of 5 Re: P0303 - next step? [crawfe1] by xwesx

Dec 03, 2012 (3:25 pm)

Replying to: crawfe1 (Dec 03, 2012 1:25 pm)
Interesting. I glazed over that part as I read the low compression information. I had a '96 Outback that suddenly was horribly rough during idle, but (like yours) was fine at higher speeds. The problem with that one was a knock sensor. But, the knock sensor failed, which did post as a trouble code (knock sensor out of spec). It ran especially poor when the engine was cold.

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