Subaru Baja 2005 misfiring on #2 at low rpm

After hooking my 2005 Baja to the computer I was told that the #2 cylinder was missing at idle. I can’t even tell. And it does not miss going down the road. Wires were checked and the spark plug was replaced. Also an injector additive was added. I’m still getting the same CEL light popping on. It happens when the engine is warmed up and I am driving around below 2000 for a few minutes rpm or at idle for a few minutes.

It sounds like wherever you are taking your car isn’t really interested in trying to diagnose the problem. If all they really did was visually inspect the wire, change THE plug and add some snake oil, I’d find a different shop. A misfire can be caused by several different things so speculating is really useless. Oh and change all your spark plugs, or put the old one back in, changing only one is goofy at best.

JMHO, but anytime an engine performance problem exists a compression check should always be performed. This is especially true of vehicle engines that have mechanical valve lash adjustments.

The last inspection/adjustment is not recommended until high mileage but this is not a good policy to follow.
The spark plug was out so spending another 60 seconds checking the compression would have been the smart thing to do.

One always weeds out the possibility of a mechanical fault first. This prevents throwing parts at it and using things like injector cleaners.

Thanks! that helps. The mechanic is going to do the compression test at no charge. what is JHMO

Yeah, I wasn’t very pleased with the changing of only one plug. for a test maybe. I was going to change the rest but I can’t find them. I imagine where they would be on a the flat 4 engine but I am not seeing them. I forgot to mention This is the Turbo model so there is a big turbo cooler on top of the engine. As for the cylinder. I have been reading that the injectors have issues. I have 70,000 on this car. Any recommendation on a book I can use to tear the engine apart?

JMHO is just internet gibberish for “Just My Humble Opinion”.

I mention the compression test for the simple reason that one should never assume that because an engine even has low mileage that everything is fine internally.

We had a Subaru come into the shop once and it would barely even start and run.
Valve lash was very tight (the reasons why were unknown) and both cylinder heads were absolutely trashed to the point of not being repairable. Valve seats and even part of the aluminum surrounding the seats was burnt out. Only one cylinder out of 4 had much compression at all and even that one was pretty shaky.
This car only had a shade over 7k miles on it so it was essentially near new.

If you get a compression reading you might post back with what that figure is and let’s examine it. Some mechanics consider a reading of 120 PSI fine and that’s not the case at all. With only 70k miles on the car, and assuming no mechanical faults, you should be looking at around 170 PSI and up.

Wow! Thats great information! I will let you know what the reading comes back as. After I got your information I called him and he will check the compression but expects it to be good. If thats the case He wants to test the injector by back flushing it or something. The mechanic told me he didn’t do the compression test because it was only happening at idle so he was assuming there were no mechanical issues and it was something simple cheap. The spark plug and the injector cleaner were very cheap and he hoped that would be the problem. So if the compression is good what would be your next step?
thanks again!

It is entirely possible to have low compression on a cylinder and the problem not manifest itself at off-idle speeds.
It can very well have a slightly rough idle that will smooth right out when the throttle is opened a bit.

At this point I’ll remain optimistic and hope that it’s not a low compression problem.
I’m only making the point that a mechanical fault should be eliminated or verifed as a first step because it’s far too easy (and has been done far too often) to throw everything but the kitchen sink at a car while attempting to make it run right. With a mechanical fault it will never run right until that fault is fixed.

It could also very well be the plug wires or even a corroded terminal in the coil pack. Checking plug wires with an ohmmeter can be a pretty iffy deal sometimes.
It’s possible to have a wire check fine and yet still cause a misfire.

There are other things that could cause a rough No. 2 misfire; coil pack, faulty injector or injector circuit, etc.
Sometimes an injector can have a bad spray pattern that will cause a problem at idle only but will not be noticeable when the RPMs go up. There is really no test for this except removing the injector and visually inspecting it (requiring some specialty equipment) or seeing if there is some anomaly on a CO machine or oscilloscope.

Well, The news on the compression is not very good. 120 PSI was the reading. ANy suggestions on this? Is there a way this could not be expensive to fix? THe Mechanic said they need to do a diagnostics. What kind of time can I expect to pay on that?