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Intermittent surging

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Looking for some advice on a problem I've been having for a while, 2005 Legacy GT. There is no check engine light on. I have an intermittent surge that comes and goes randomly. It can often happen while accelerating and comes with more extreme surging, and sometimes if I'm cruising on the highway I can feel the car lightly rocking back and forth. While cruising at a constant speed I don't see the RPMs jumping up and down, and if they are it's such a small amount that it's not noticeable on the gauge. It doesn't seem to surge at all when idling.


For some background, the issue started a while back when I went through an automatic car wash and it included and undercarriage wash. Check engine light came on shortly after, which came back to a bad knock sensor, and I replaced that. But have still had the problem ever since then.


I have just had the spark plugs and coil boots replaced; the mechanic said the coil packs looked fine. I have replaced the MAF sensor. None of this has helped at all.


I'm hesitant to take it to another mechanic, I've had it in to the dealership and another mechanic, and with the problem being intermittent, no one can find the issue or even agree with me that there is an issue.

Edited by CataLYTic
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There's a thread here about "surging" it normally happens on these cars between 2400-3000rpm.


I'll try and find it.


Most of us have installed a T fitting in the small line off the BOV and connect that vacuum hose off #4 intake runner to it, reset the ECU drive the car. That gives the fuel pressure regulator a cleaner consistent signal.

Edited by Max Capacity

305,000miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. CHECK your oil, these cars use it.


Engine Build - Click Here

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