forester Intermittent missing like issue

[kingofnerds]

I have a 2005/6 2l Petrol

I can't establish a pattern of any kind to this.

 

The problem is:

 

Feels like a misfire, but it's only evident on load and with mid range throttle

You can drive the car carefully on low throttle (so long as there are no steep inclines to overcome) and it would be difficult to notice a problem

You can floor the throttle past the mid range and it may cough a splutter, particularly if the revs are a little low, but it will rev through the splutter and go...

Tell you what it reminds me of is: When in the old days, when damp used to be an issue on the HT leads and it would be earthing out to the engine block

But basically it idles nicely and there is no management light on

It's been on a diagnostic but at the time it was running normally. And of course nothing was showing as an issue.

I just did 1200 miles to the very North of Scotland and back home to the Lake District, it was perfect all that time, then suddenly after a brief stopp, the problem started. Was like that for a couple of days covering maybe 150 miles and then it's gone again.

 

Suggestions welcome. Thanks

 

[Mr B]

First thing I would do is new set of leads & plugs.
Leads on these play up a lot & I get at least one a month with similar faults & it cured with new leads, even had car in that was on subaru diagnosis & not pinpointed fault so before waste money on further diagnosis labour try leads as easy do yourself & even plugs if you can manage them.

Give seller a call to confirm parts right as makes easy return should things be wrong >

http://www.ebay.co.uk/itm/Fits-Subaru-Outback-Legacy-Impreza-PROSPARK-OES1229-Ignition-HT-Lead-Set-/400599297283?fits=Model%3AForester|Cars+Year%3A2006&hash=item5d45942d03:g:lisAAOxyDEVSc7ni

[kingofnerds]

Plugs look good TBH, we did check. We thought they might have been missed because they are a little awkward to do.

But my Son was thinking coil leads too

Good call I reckon

Thanks

[Mr B]

leads are common one for fault when likes of 10 years+ old, one forester I bought had slight miss when on test drive & think part of reason was for sale & had some bills that looked likely it been playing up but issue not found, I took chance & £20 new leads cured it .
Those prospark leads are ok for price, I used few of them & found them as good/better ends than blueprint ones.
Not always the case but at price it worth ruling out before digging deeper .If still present do plugs too as may have bad insulation on one even if look perfect, set of Bosch plugs for example are very cheap too on eBay so if not the plugs it not big money to rule out & kind of handy have set spare .

 

[kingofnerds]

Thanks

I'm planning on doing this, but it may be a time before I get to it.

[kingofnerds]

OK

Long story. I went to TEG Motorsport in Carnforth. I live near them.

I had to wait for the missing to be present and it be convenient for me and them to take a look. All this happened recently and they plugged in. Nothing was showing faulty but they could see the issue presenting itself on the diagnostic during a test drive. Their experience put it down to the Knock Sensor. This was replaced and has greatly improved the problem. Virtually no miss at all, just very occasionally a very slight hiccup on very slight throttle only.