The Stuttering Subaru

For the past month or so I’ve had an issue with my 2005 Subaru WRX where the engine likes to stutter for a split second when revving from idle. The issue is not consistent, it happens the most when I apply throttle from an idle but it also happens occasionally when I try to rev match. I replaced the injectors about 2 months ago for a misfiring issue - however I feel as though the stuttering problem may be somewhere in the fuel system. My initial thought is to replace the fuel filter but I know there’s people on here with more experience than myself that may have a better suggestion so any advice would be appreciated!

My first thought was that instead of touching your injectors (which rarely fail) why didnt you go toward a simple tune up first? I believe this engine still uses spark plug wires… they are often overlooked and left on a vehicle until failure…and that failure mode is sometimes maddening and intermittent when they begin to deteriorate.

I would have gone for spark plugs and wires far far far before ever touching or even suspecting an injector. Unless engine codes told me otherwise. In fact that is what you should be doing now. Plugs before wires…see what happens…still there? Then do the wires…

Any engine codes associated with this or is it outside the engine computers knowledge? (like plug wires would be)

Do the basics and let us know… Spark plugs…and then wires… Or you can do them both at the same time and not know which solved the problem. Some people don’t care about root cause, but its sort of a “thing” with me…so I do things incrementally and in the end I can state with clarity what actually caused xyz problem.


The car is running a COBB stage 2 tune. I didn’t jump straight to injectors, I tried plugs and wires and coils until I tried injectors and that solved the problem. That being said, do you suppose the plugs or wires could have gone bad in the last 2 months?

Also - injectors on these cars fail allllllll the time. I had to order them on back order because it’s so hard to find a website that keeps them in stock without charging through the roof.

Just for grins, clean your throttle body using a can of Throttle Body Cleaner (not carb cleaner) and clean your Mass Airflow Sensor using a can of Mass Airflow Sensor Cleaner. So cheap to do and I’ve solved drivability problems by doing it.

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Wow… that is quite a lot of information that could have been very useful to …say, a mechanic, who is trying to help you via an online forum…

Didn’t think I’d need to clarify that I replaced the injectors because they were faulty and not because I just felt like replacing some injectors

The Key piece of info is the Tune…not that you replaced injectors. Have you had any of these injectors tested? In what manner do they fail?

I’ve been doing this stuff a very long time and never seen injectors fail “all the time” before… It begs the question on just how this tune is running the injectors and or what the failure of these injectors actually is for that part number…and it seems multiple part numbers. Just a thought.

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I will try to be as clear as possible:

I did not do the tune myself, the tune was installed by a credible shop when the previous owner had it. All I know about it is that it is a COBB stage 2 tune. Admittedly tuning is something I am very unfamiliar with. I’ve been hesitant to take it to the shop, mostly because I hate the idea of spending $500 for them to make a few small changes on a computer and maybe 2-3 hours of labor at most. If you think this is my best option though I’ll re-consider it.

As for the injectors, my car had a misfiring issue. I tried cleaning/replacing the MAF sensor. I tried replacing spark plugs, and I tried replacing the ignition coils. None of that solved the misfiring issue. When I replaced the injectors, the car stopped misfiring. I do not have the old injectors and I do not know what caused them to malfunction. The injectors I purchased were OEM spec Injectors ordered from Summitt.

I can look at the tune settings on the Accessport - is there anything specific I should look for? Everything (looks) fine, but like I said I’m not the most familiar with tuning an engine.

Additionally, this was the first time the injectors failed on my car. I had just heard many times that Injectors are prone to fail on these cars, and it was very difficult to find OEM injectors to purchase - maybe because 80% of the owners run hot tunes on them.

Granted, this problem could be due to any one or more things.

What would I do if the car were in front of me? I’d connect a vacuum gauge to get a handle on what is going on internally.
Depending upon the gauge results I would run a compression test; which I do whenever the spark plugs are out. Ideally, vacuum gauge readings should be in the 20-21 range and compression in the 185ish range on all cylinders.
One cylinder down a bit (possibly due to a neglected valve lash inspection) can be enough to cause an off-idle stumble.

I’m a bit baffled by your comment about these cars being prone to injector failure. Maybe the fuel system is contaminated. Larger debris gets caught in the fuel pump sock. Next size down debris gets caught in the fuel filter. The finer stuff that manages to get through gets caught in the fine screens inside of the injectors.

Just some misc info that you may or may not be able to use but if the car were mine a vacuum gauge would be Step One for me. It’s an invaluable little tool IMO>

I forgot to mention that I DID run a compression test on all 4 cylinders (back when it was misfiring and before I replaced the injectors) compression is fine. Unfortunately, I’m well aware that there are many things that could be causing this issue, I’m just seeking any advice possible because I am out of Ideas. I haven’t done a vacuum test, I can definitely look into that. Luckily I’ll have a 4 day weekend for the holiday so maybe I can spend some more time digging deeper into the problem. I do appreciate all the feedback I’ve gotten so far.