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05' LGT: RPM "hunting" between 1500-2000 on constant throttle, no CEL?!


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Hi All,

 

My 05' Legacy GT has been acting up. First, at cold idle, the RPM jumps up and down in an unusual and cyclic way. Then when I start accelerating and cruising, between 1500-2000 RPM, the RPM is "hunting" (or jumping up and down) even though I have a constant throttle position. You can feel the power surging in a cyclic way. Finally, when I give more gas, the car downshifts and powers normally through 3000-5000 RPM with boost no problem.

 

Unfortunately it hasn't kicked a CEL, so the fix isn't obvious. Replaced spark plugs, air filter, and checked the throttle, seems clear. Unplugged the MAF and car ran okay at first, but the problem started again, so I doubt it's the MAF. I wonder if this might be a bad O2 sensor, throttle position sensor, or cam position sensor, but hard to tell without a check engine light...?

 

Before I start ordering new sensors, has anyone experienced a similar issue? Thanks in advance.

 

Taylor

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Another thing to do would be check your learning values with romraider if you have the tools. Or with an access port. Then you could also look into the deeper stuff and see if your afr is doing weird things (bad o2 sensor) or you're having knock and it's pulling timing or something weird. I think with those you can also look to see if the trans sensors are acting weird.
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Hi All,

 

Thanks for following up. I unplugged the front O2 sensor (even though no CEL was kicked), and the problem seems to have subsided. This leads me to believe it's O2 sensor related, so I am thinking I will replace both front O2 sensors, and see how that goes.

 

Any insight on replacement part? Looking at either the Denso OEM or the Walker part on rock auto...

 

Cheers!

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Thanks gkinslow. So the Denso OEM (#2349120) is a good bet? I was checking out the Walker (#25054058) as it's a bit cheaper and my friend has done exhaust replacements with their parts before, but I certainly appreciate your advice! Don't want to mess around with a junk O2 sensor.
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305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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For the oem vs non oem thing, my civic only gets oem ps and mt fluid cuz they are a weird formulation, nothing else because it's an inexpensive vehicle with no power and a tiny engine.

 

The outback gets a lot more, almost exclusively oem stuff. The increase power output and engine size along with all the ecu adjustments due to the turbo make it more sensitive to parts performing at only 90% where the civic might not notice of the parts only kinda work.

 

These cars seem to have lots of stuff like that. Sensors, axles, various suspension components

 

 

Sent from my iPhone using Tapatalk

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