WTH is wrong with my daily?

[HLxDrummer]

Alright guys, who can figure this out? 2007 Forester with 70K on it. Was running great until a few weeks ago when it started missing at idle (will run smooth, then miss once or twice then be smooth again) and sputters at low rpm under load. High RPM and WOT it is fine. Had a CEL for cylinder 4 misfire.

Hooked up the logger: IAT, TPS, MAF, coolant temp sensor, idle switch all seem to be working fine. Rear O2 was stuck at 0.85 at idle. If I stabbed the throttle it would cycle. I couldn't read the front O2 for some reason.

Already changed plugs and wires. Also swapped coil packs with a known good condition one.

Any ideas? Here are mine:

Injector: Only thing left I can think of that explains only having a problem on cylinder 4. Considering switching this injector to another cylinder to see if the code moves. Just need to buy new seals.

EGR: If stuck open, it could explain the rich O2 at idle, but I've heard it's rare to get stuck open, and it doesn't explain the cylinder 4 misfire. Considering swapping for the one off my wife's car.

Dirty throttle body: Heard it might cause this problem.

O2 Sensor: Not sure if this is the problem or if it is reading strange because there is another issue.

I would be grateful for any ideas. Don't particularly feel like throwing parts at the car/spending $100 on new gaskets to swap parts between this car and my wife's if I can help it lol

[Jesters Deadd]

I would guess injector.
I would pull it and clean it.
I have a friend that uses a sonic cleaner on injs and it has woked well for him.

[RealMcCoy]

Front O2 is most likely an air/fuel sensor, (wideband) generic logger probably doesn't know what to do with the signal. Rear O2 is supposed to be pretty steady providing the catalyst is working properly, and has good oxygen storage. If it goes into closed loop, and the fuel trims are in line, I wouldn't worry about a fuel control issue.

Injector or injector connection could definitely be a possibility, those motors are also well known for the valve guides moving around causing misfires.

Have you checked the valve adjustment?

[box]

Unplug the alternator and then start it up, blown/partially blown alternator diodes causing an idle/low load engine miss (sometimes accompanied by cam/crank sensor codes) is fairly common on Subarus. Also check the multi-plugs for the engine harness for poor connection/corrosion.

You should see an injector fault on the spark plugs.

[Chris@Rvengeperformance]

Have you done a compression check? My brother's legacy gt really liked eating valves and he had about your same mileage.

[HLxDrummer]

Thanks for all the info guys, really helpful. Didn't know the rear O2 should be steady or the common Suby issues. I tried searching my hardest but couldn't find anything great so thanks for that.

I haven't checked compression. I thought about it but figured with low mileage and good high rpm performance that everything would be ok internally. I would check on that, though. I'm not sure how to check valve adjustment but I'll look into that, as well.

My wife's legacy engine blew it looks like from a cracked valve guide and chewing through the oil. My dad just replaced a Suby engine in his friends car, too. Making me a little nervous!

[HLxDrummer]

So switching the injectors didn't help. I do have two questions. Would a compression test or leak down be better? Compression sounds easier but not sure if it will pick up all issues the leak down would. Also, should I unplug the alternator at the actual plug with multiple small gauge wires? Or at one of the terminals?

Thanks!

[Chris@Rvengeperformance]

A compression test will tell you that you have a bad cylinder. A leakdown will narrow the prob further.

What's wrong with the alternator?

[RealMcCoy]

Just pulling the connector at the alternator will disable it.

A compression test may pick out things that wouldn't show on a leakdown.

I'm not confident either would find your issue due to it's intermittent nature.

Adjusting the valves is a needed maintenance item that I would do first just to rule it out. A tight valve can cause compression and leakdown issues anyway, and possibly send you in the wrong direction if not caught.

If the valve guides are moving around, there's about a 99% chance it's the exhaust guides. You can visually check their position by dropping the exhaust and looking up the ports.

[HLxDrummer]

A compression test will tell you that you have a bad cylinder. A leakdown will narrow the prob further.

What's wrong with the alternator?

Ok that's awesome. I'll start go with the compression test first just to see if there is anything going on.

The reason I was looking at the alternator is because box mentioned it above. Figured it is easy enough to unplug it and rule that out.


Just pulling the connector at the alternator will disable it.

A compression test may pick out things that wouldn't show on a leakdown.

I'm not confident either would find your issue due to it's intermittent nature.

Adjusting the valves is a needed maintenance item that I would do first just to rule it out. A tight valve can cause compression and leakdown issues anyway, and possibly send you in the wrong direction if not caught.

If the valve guides are moving around, there's about a 99% chance it's the exhaust guides. You can visually check their position by dropping the exhaust and looking up the ports.

So the next thing you would do would be to adjust the valves? I was going to try to do that later on my list since it seems like a more involved process. I wasn't aware that was a maintenance item. I will look into it a little more and see what all I need to do.

[HLxDrummer]

Alright here's a little update: Found a ground wire on the driver's side from the engine to firewall that wasn't connected. Connected that to the intake manifold (not sure if that is where it is supposed to be or not) and it fixed the problem. Few weeks later it came back. Looked under the hood and one of the bolts holding the bracket on (the one this ground is attached to) was missing. Figured the ground isn't getting good connection now so I attached a few alligator clip wires directly from the head to the battery (all I had on me) with no difference. Checked the continuity between the ground and the head and it was pretty good I think (couple of ohms - the multimeter beeped for what that's worth). Also tried unplugging the alternator which didn't help. Compression all within normal limits. Battery voltage good and steady.

Where would you go next? Any ideas? Think I'm going to try connecting a jumper cable from the battery to the block just to be entirely sure it isn't a ground issue. The car runs normal on the highway/high RPM. It also seems way worse when the car is cold or if I let it idle a while.

[HLxDrummer]

Well the car is still having the issue (as well as a bearing noise from the back and intermittent AC issues...). I pressure tested the intake looking for leaks tonight. Disconnected the PCV hoses from the intake and plugged the intake. So the two PCV hoses were connected to the heads and venting to atmosphere. Went to pressurize the intake and all the air comes out of the PCV hoses. I'm assuming this isn't good... right? Only thing I can think of is bad rings or piston or something. Compression tests was great though...

[DocWalt]

I'd bet on you missing a PCV hose on the intake manifold somewhere. Subaru tends to put them on the bottom of the intake manifold.

I'd also bet on a ground issue somewhere, but I don't know :(

[HLxDrummer]

Ya I think your probably right. No way the car would be running this well but that much air going past the piston. And not smoking. I left the PCV valve on the manifold and just clamped the hose afterwards - maybe I didn't clamp it well enough/the valve is bad. I also noticed there is an electrical plug going to the valve which I thought was weird... maybe it doesn't just close with pressure like on the 3/S?

Also I noticed the EGR valve wasn't leaking when I pressure tested and I was thinking that may be the problem (stuck open sometimes), so I unplugged it and have been driving around a few days and the hesitation is gone. Gunna drive it a few more days before I call that the problem but I'm hopeful!

[DocWalt]

Bad EGR valve would definitely cause some hesitation if it was opening under incorrect conditions.

[HLxDrummer]

Just wanted to update incase anyone else had the same issues. I replaced the new plugs from the auto parts store (name brand but can't remember which ones) with factory plugs. Problem fixed.

I was also having trouble with my AC running for a while then the compressor would disengage and not re-engage (the AC light on the dash would stay on). If I turned it off and on immediately it still wouldn't work. If I turned it off and left it off for a while it would then turn back on for a little (longer I left it off, the longer it would run next time). If I jumped the wire for the AC clutch under the hood it would engage and run indefinitely (after about an hour it would not be as cold, probably cause the compressor isn't designed to run non-stop). I took the clutch off the compressor and removed a little spacer (looks like a washer) and put it back together to close the clutch gap. Now works like a charm. For more info see this page: http://www.subaruforester.org/vbulletin/f87/how-adjust-c-compressor-clutch-116835/

[DocWalt]

That's a pretty neat fix and way cheaper than buying a new compressor/clutch assembly!