2005 Subaru Legacy GT shudders only when accelerating

Hello All,

 

Recently my 05 Subaru has been doing a weird shudder when I press on the gas. It is almost like a delayed response, but even when it begins to kick in, it will jitter the whole time I am accelerating. The worst part is, that sometimes it will be a good full acceleration, and other times experience this issue (I would say the issue happens 80/20 of the time). No check engine light has ever come on. Here is some info on my car:

 

 

• 2005 Gt Limited
  
• Around 115,000 Miles
  
• Recently got the Timing belt and other belts replaced along with my radiator (was happening before these were replaced)
  
• Replaced all air filters recently and cleaned the front air filter sensor on top of the air intake.
  
• My friend and I did some testing and replaced the back O2 sensor. The issue stopped after replaced this part for about a week and had smooth accelerations, thought issue was resolved, but now the jittering is back.
  
• Oil was not the issue, got full synthetic in it recently as well.
  

 

It seems like the turbo will pop in and I will get a burst of acceleration but then it will keep jittering along my accelerations. Car runs super smooth in idle and also just cruising at any speed. Issue ONLY happens in acceleration and appears to be the worst in 2nd and 3rd gear. Let me know if you need more info or if something doesn't make sense!

 

Thank you anyone that can help or have had this issue!

I had the same problem, when my mechanic replaced my turbo. When it happened, I pulled over to investigate and found that the two bolts that hold the intercooler down to the compressor side of the turbo were finger-loose. This situation was just a boost leak. I tightend them up with a ratchet and was G2G. If you havent removed/replaced your TMIC, this probably isn't the case, however ill bet you have a boost leak elsewhere. Check all of the Vacuum lines. Hopefully you will find the culprit within one of those vac lines. This colored vacuum line diagram posted by Boostin should help: http://legacygt.com/forums/showthread.php/2005-2006-lgt-colored-vacuum-routing-diagram-143225.html

Hey 762x39 thank you for your response.

 

I just called the mechanic that put in my belts and I asked him how much it would cost to run through my engine and check for these issues you are listing. He told me he already checked all of the vacuum lines and bolts to make sure there were no leaking issues like this (I told him about this issue when I was getting my belts fixed to see if he could find the problem). His advice was to monitor and if it got worse bring it in or just wait for the check engine light to come on.

 

Sigh. I guess I would rather not wait. Could it be that the turbo is just getting old and these are the symptoms? If I had to describe what he feels like, these are the conclusions I could come to:

1. It feels like the engine is not getting the correct air/fuel ratio, it feels like its getting intermittent readings, causing the random jittering.

2. The turbo is either getting old or misreading the amount of air coming in and supplying the wrong amounts to the engine, thus causing these Jolt feelings of energy and then no energy. It's like the turbo turns on and then turns off and does that all the way through the acceleration process till I shift again.

 

Sorry for rambling, hopefully that was clear.

Get a cable and do some logging/pull an lv, will show your a/f ratios. Also do your own vac/boost leak test. I made a tester for a few bucks with home depot parts.

Are you sure the check engine light works on the car, so with key on and car off, does it light up? Go to autozone and ask them to just pull codes, don't tell them the light is not on.

Sounds like a misfire, coil or plug bad maybe.

The '05 is notorious for the 2 - 3k RPM stumble. So far, we have narrow it down to a few issues, but each car is a little different with this.

 

1) The front O2 sensor (A/F ratio) is defective OR it's aftermarket. Some of the aftermarket sensors will cause this. Recommend OEM sensors.

 

2) Replace the fuel regulator with an aftermarket or OEM STI one. There is a walkthrough on how to do this.

 

3) If stock, have a tuner review your logs to determine if the A/F ratio needs to be corrected.

 

These are the most common fixes to this issue.

^ Yes.

 

Just to elaborate a bit here, but i'm also here for some information as well. My car does this to a degree, MY05. It's terribly annoying. One thing I want to add is, check your turbo inlet hose, this is a common failure point on these cars.

 

1) Denso 234-9120 is the OEM sensor. These sensors go bad frequently, and may begin to fail without throwing any type of CEL. I had a P2096 code that went away after replacing my front O2. I threw the code a few weeks ago, but I cleared it and it remained off with no pending.

 

2) I believe you can use a fuel pressure gauge to test if your FPR is bad, though I have never tried to install one. To my knowledge, the Cobb FPR fits on the LGT application. (REQUIRES RETUNE)

 

3) If you have a tactrix, pull a learning view, you'll see if your fuel trims are off, i'm willing to bet it's probably a vac leak.

In my case 2 left coil packs went down. It started as shuderring under load but finally engine was barely running and vibrations were terrible.

 

Krzys