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Impreza Poor acceleration, misfiring

8 messages,  Last post on Aug 13, 2010 at 10:22 AM

You are in the Subaru Impreza Maintenance & Repair Forum.

What is this discussion about? Subaru Impreza, Engine, Sedan

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#1 of 8 Impreza Poor acceleration, misfiring by munous

Aug 10, 2010 (11:18 am)

I have a manual transmission 1995 Subaru Impreza with 180,000 miles, but runs perfectly. Almost.
 
It idles well, but has just started bogging down under acceleration and loses power. It starts backfiring, shaking and won't go over 40 mph. If i give it gas while idling, it revs fine and sounds normal.
 
Timing belt is fairly new, as are spark plugs.
 
Any ideas?

#2 of 8 Re: Impreza Poor acceleration, misfiring [munous] by xwesx

Aug 10, 2010 (11:32 am)

Replying to: munous (Aug 10, 2010 11:18 am)
Sounds like a timing issue under load. The '95 is, I believe, controlled by crank, cam and knock sensors. It may be that your knock sensor is not up to snuff. Also possible is that your plug wires are aged and have too high of resistance, but I would expect the car to stumble a little during idle and while revving if that was the case. You can check the wire resistance easily enough with a multimeter.

#3 of 8 1.8L Knock sensor by munous

Aug 10, 2010 (12:40 pm)

I've been looking for a replacement knock sensor but can only find one for the 2.2L. I have a 1.8L- does this engine have a knock sensor?

#4 of 8 Re: 1.8L Knock sensor [munous] by xwesx

Aug 10, 2010 (1:12 pm)

Replying to: munous (Aug 10, 2010 12:40 pm)
Ah; I didn't realize Subaru used the 1.8L in 1995! I assumed it was a 2.2.
 
I am not sure what retards the timing on the 1.8L. Did this problem happen just after a timing belt replacement or has this simply cropped up at some point since then? If it was just afterward, the timing could simply be off a tooth or two (easy to do), but if not, it is likely a sensor or control module that is acting up.

#5 of 8 rough idle too by munous

Aug 10, 2010 (1:42 pm)

The timing belt was replaced 20,000 miles ago. This problem started after i replaced my starter. My wife thinks it was occurring before that and now its just worse. It is now undrivable.
 
I just started it again and it does seem to be idling rough now.
 
I am not finding any knock sensor replacement for the 1.8L, what other sensor could cause this?

#6 of 8 Re: rough idle too [munous] by xwesx

Aug 10, 2010 (5:10 pm)

Replying to: munous (Aug 10, 2010 1:42 pm)
Since it seems to have become worse after changing the starter, check to make sure you have a solid ground (the main grounding strap tends to connect at/near the starter). Also, check the resistance in your spark plug wires to see if they are within spec. Do you have a Haynes or other repair manual for it? If you do, that will have the resistance specs....

#7 of 8 Solution! by munous

Aug 12, 2010 (6:56 pm)

I have had the car for 2 years and never changed the wires or fuel filter so I just bought both at napa. I tried the filter first and that wasn't it. Then replaced the wires, and it's running like a watch again. Thanks!

#8 of 8 Re: Solution! [munous] by xwesx

Aug 13, 2010 (10:22 am)

Replying to: munous (Aug 12, 2010 6:56 pm)
Fantastic! I went through a similar scenario on my '98 Escort last Spring. The only difference was that I was so convinced it couldn't possibly be the wires that I ended up taking it to a shop for diagnosis. My $45 wires turned into a $300 expense.
 
Lesson learned.

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