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2008 STI - hesitation at 4000 rpm?
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Old 02 Oct 2012, 02:24 PM   #1 (permalink)
Fresh Scooby
 
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2008 STI - hesitation at 4000 rpm?

Hello all,

Having some problems with a 2008 STI... before I bring it in to a stealer (or yield to temptation, have it taken apart and rebuilt), I'm wondering if there is anything that I can do to get things solved more cheaply and avoiding bigger problems down the line.

Problem: the engine runs very roughly from about 4000 rpm to red-line. It's very easy to feel this in 5th and 6th, in 3rd and 4th it feels more like a flat spot, but when the engine has more time to rev up it's definitely felt as hiccuping and start-go as if the ECU were cutting fuel or the wastegate were chattering or sticking somewhat.

The engine is regularly fed and watered only on Shell V-Power, and it has just had a regular 40k miles service (new plugs, filters, fuel filter, whatever else) with no faults noted. The car has never been mistreated, is warmed up slowly and left to cool for a minute or so with the engine on if I have - erm - been naughty.

Also, due to an idiot coming out of B&Q and leaving half a 4x2 joist planted in the radiator the car has a new rad and a/c heat exchanger, but I don't think it would have anything to do with that.

As I mentioned above, I'm trying to at least reduce the span of possible faults, but have very little idea of what *could* be happening given I don't know the weak spots of the STI. Things I have thought of are:

1. Wastegate /ECU management problems
2. Wastegate mechanical problems
3. Fuel pump/filter problems (is there a secondary fuel filter that I can check? The problem seems to be more noticeable when there is less fuel in the tank, though I generally fill up when gauge is at 1/3 or so)#
4. Spark plugs (which the logbook shows as "changed" - but did they?)
5. Air mass sensor going and/or cats getting stuffed (though I would expect the same issue to be present in low gears?)
6. Turbine / turbo bearings about to collapse - though there is no whistle or noise.

Before I start taking things off at random (and then end up with a non-running car), any words of wisdom as to how I can narrow down the options? Is there something that I have missed and is likely to be "it"?

Thanks in advance!
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Old 04 Oct 2012, 08:25 PM   #2 (permalink)
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Re: 2008 STI - hesitation at 4000 rpm?

My 2003 sti acts in a similar way and its the neutral position switch on the top of the gearbox thats faulty. It momentarily thinks the car is in neutral when accelerating and cuts the power, it does it so quick that it just feels a bit jerky sometimes. I guess the 2008 has one too, so maybe its that.
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Old 04 Oct 2012, 08:43 PM   #3 (permalink)
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Re: 2008 STI - hesitation at 4000 rpm?

Thank you! Will check that too (starting from finding out if the switch/sensor exists!)
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