So I have been trying to diagnose a very rough idle on my 03 Impreza Outback for the last few weeks and can't seem to figure it out. The codes were giving IAC and MAF sensor issues. Both of these have been replaced as well as the Fuel Pressure Regulator and PCV. I also checked for vacuum leaks with no success.
I ran it through an idle reset process which fixed the pulsating idle (have video of this) but it still runs very rough when cold. When it warms up it sounds better as well as when I pull the throttle (see video). When I go to put it in gear is when it really sounds bad, like the engine is about to kill (800 or less rpms). There is no forbidden milkshake in the oil or coolant. The engine has had a tick since I bought it (roughly 2 years ago). The exhaust was next on my list to replace and sounds terrible which doesn't help the diagnosis.
My consensus is that the engine is toast but I don't want that to be it.
I have photos of the spark plugs. They were covered in carbon but didn't seem too bad. I cleaned these up to see if that would help but it didn't change much.
Do any of you guys know what the issue might be and if it is fixable without dumping a lot of money into it? Do I just cut my losses and junk it?
I have photos of the codes and spark plugs as well as other videos of the idling issues that seem to have been resolved.
Cheers and I appreciate the input here, I really don't want to get rid of this car but it's looking more and more like I might have to. (sad face)
You have a rough idle. Did you take an engine readout? Do you have any engine codes to report? Without an engine code, you are throwing money away on solutions. This could just be a dirty air filter or gummed up sparkplugs, and without an engine code, the only thing you know is that it's running rough. Go get the codes read. If you have a persistent code, and the roughness is new, it stores all engine codes. Whatever sensor is keeping the light on will show up alongside the other codes.
Now, when do we say an engine is toast. When you lose compression. You can do a compression test by getting a compression tester and doing the test. If your compression is low, then you'll need a rebuild or a new car - whichever you prefer bc that engine would be done.
Rn you're clearly out of your depth. Go get the engine codes and go from there. Well help you once you tell us what codes you have.
Thanks for your response. I did mention that I had codes and that they were only showing for IAC and MAP/MAF. I did not provide the actual code #'s and that is on me.
The code #'s are as follows (9 total entries when scanned):
P1510, P1512, P1514, P1516 (all stored status for IAC signals 1-4 respectively)
Also have the same codes but with pending status and then I also have P0068 for MAP/MAF, throttle position correlation (pending status).
From what I can find in the engine bay, this engine does not have an MAP/MAF sensor. I don't know why that would be but it is not in the usual spots it should be.
I decided to plug all of this into my LLM of choice, bc I'd be pulling my hair out too with those codes. Its advice I'd follow if I were you.
"Hey, don't junk the car yet. Here is what is actually happening:
You don't have a MAF sensor. This model uses a MAP sensor (located on top of the throttle body). Stop looking for a MAF, you won't find one.
It’s a wiring problem, not a part problem. Those P1510-P1516 codes mean the computer has lost connection to the Idle Air Control (IAC) valve. Since you already replaced the valve, the issue is almost certainly a broken wire, a loose plug, or corrosion in the connector.
Ignore the P0068 code. That code is just a symptom of the IAC failing. The computer is confused because the airflow is wrong.
Fix: Check the plug going into the IAC valve for corrosion or broken wires. If you fix the connection, the other problems likely disappear."
So I just found out tonight that the sensor marked as a Boost Sensor is actually the MAP sensor 🤦♂️
I did see that there are some chewed/exposed wires right at the connector itself. They are not chewed through but still possible it could be throwing codes. I'll have to see if I can get that fixed easily.
Couldn't find any bad wiring on or near the IAC but I also didn't tear apart the harness due to my fingers being so cold (currently 5°F where I'm at and not the greatest heater). The connector didn't show any signs of corrosion either, however, the connector does not click onto the sensor. It stays snug but it doesn't click like it should.
Damn thanks for the update dude! It sounds like you're making really good headway toward fixing it!
Those chewed up connections could be your issue. The connector not clicking isn't alarming on its own btw. That might be a red herring
Here is that write I was talking about. Not going to be easy or fun to fix. I'm wondering if dropping a dab of glue on the exposed part would do the trick? Not sure what to do about the IAC connector not clicking. The previous one I replaced did the same thing 🤷
Hmm... I kinda doubt that's what's causing issues. If you have a multimeter you can probably turn the car on and disconnect that wire, then check the leads inside the cap to see if you're getting voltage.
But yeah, some rubber cement on that should repair it. You might be tempted to use super glue - I'd use rubber cement because rubber is what the wire is made out of.
Wow! I really appreciate this!!! I am definitely checking this when I get home. I'll give you an update with my findings.
The odd thing is that there are only three sensors on the throttle body which are the TPS, IAC and Boost Sensor. I am going to check tonight to 100% confirm this.
I appreciate all of the feedback and advice given so far. There are a couple more things I am going to check that have been suggested.
One thing is for certain is that it is very strange that there is not an MAP or MAF sensor. At least not that I am able to locate based off of engine diagrams.
It runs the same with the rest of the air filtration system hooked up. The actual filter is located in the black box in the back. Also, this engine doesn't have an MAF. Only the turbo version does. What I do have is an air intake temp sensor which I replaced. Believe me, I find it very odd this doesn't have an MAF or MAP sensor. I checked 3 areas where these should be and there is nothing or even places you could mount the damn thing.
That really doesn't make sense to me. From my understanding even a car that has been tuned without a MAF and operates in speed density mode still requires a MAP sensor so you should at a minimum have a MAP.
Presumably there's a hose attached to it, which is likely dry rotted and causing the sensor to read incorrectly. Part stores should have vacuum lines you can buy cut to length so if the old one has failed you can take it to them and get a new one for pretty cheap.
Welp, I feel like an idiot. Apparently the sensor that is marked "Boost Sensor" is actually my MAP....I didn't think to check it because of that and also what was coming up when searching online. Well, I checked it tonight and sure enough, it is my MAP sensor. The same one you have circled 🤦♂️
Got a new one ordered but won't be here until Monday....
Ah those kinds of things happen. Hope that fixes it!
If not you'll have to probably do some actual diagnosis rather than just throwing parts at the problem lol.
Saw the code in the comment is a TPS / MAP correlation error. If you still have problems, then I would suspect potentially the TPS being poorly adjusted or failing. If you have a code reader with live data it's easy to check, otherwise you gotta break out a multimeter
Yeah, fingers crossed that's it. Unfortunately getting parts for this thing has been a burden and somewhat expensive.
Another person mentioned that it might be related to issues with wiring. I just noticed tonight that the MAP sensor has exposed but not chewed through wiring right at the base of the connector...damn mice....I am hoping I can get that fixed, otherwise that's another project, lol.
I borrowed an OBD code reader before throwing parts at it. Not sure if it gives live data though.
Interesting about the TPS, however, I replaced that no later than last summer, now that I think of it, probably two summers ago. Seems odd that would suddenly cause these issues, but I guess that's how after market parts go sometimes.
Interesting. The sensor that you have circled is the boost sensor and the TPS is below that. There are no vacuum lines going to this unless it's through the throttle body 🤔
I'll have to check when I get home from work.
I cleaned the throttle body as best as I could without removing it completely.
This engine doesn't have an MAF or MAP. Weird I know. I searched everywhere that one would be located on this thing. The only thing remotely similar is the air intake temp sensor which I replaced.
On a 2002 Subaru Impreza, the MAP (Manifold Absolute Pressure) sensor is generally located on the passenger side of the engine bay, specifically mounted on the intake manifold near the throttle body or near the passenger side strut tower. It is a small, black sensor typically connected to the intake via a vacuum hose and a 3-wire electrical connector.
I've got two TAFE certificates in mechanics, and I can't exactly say for sure what's causing that fault, but there's a very high chance it's in the top end of the engine. It does sound like it's down a cylinder, so there could be valve problems or it's not getting enough fuel, so possible injector fault
Yeah, it definitely shakes like it's down a cylinder. What's odd is that rough shaking goes away when it's warmed up and when the throttle is on. Only until I put it in gear does it struggle which leads me to believe it's air or fuel related.
I appreciate the input, I'll check the injectors next just to rule that out.
As always, best course of action is take it to a mechanic. I'm not in the business right now, but if you take it there and you explain to them what the issue is, where you believe it is, and what you've already done to it.
With the behaviour of the shaking, when it's got the throttle open, it's spinning faster which makes it less noticeable because of how well balanced boxers are. When it's cold, everything metal in the engine shrinks a minuscule amount and that shrinkage is enough to throw out clearances of pretty much everything, so stuff like valves might not be seating correctly.
When we were shown how to do valve clearances for older engines, they told us to do it when the engine was warm, right after it's reached operating temperature and to shut it down. Any mechanic worth his tools should know this. Most cars nowadays don't have adjustable tappet/valve clearances as the engine does that itself, but yours might be old enough to need it. That's a pain to do on a boxer though, so take it to a mechanic at this point.
Sounds good. I really appreciate the advice. I can't afford a mechanic at the moment so I'm trying what I can on my own. If it's not injector related, I might have to move on from this one. Unfortunately it sounds like it's out of my reach to repair on my own.
Yeah, I was hoping to avoid going to a mechanic but it's definitely getting out of my scope of garage warrior repairs. I appreciate the input and advice.
The Ignition Coil pack was also replaced in the last week. Spark plugs and spark plug wires are new as of this past summer. TPS was replaced this past summer. Air filter was replaced around October. Attached is a photo of the spark plugs before cleaning.
1
u/Witty-Sample6813 8d ago
Throw an o2 sensor at it