06 Subaru Outback XT Stall

As the title suggests, I have a 2006 Outback XT, which recently started shuddering (like it wants to stall) at idle… At least that’s how it started. I noticed it for a few weeks but with no check-engine light, and no error codes cropping up, I kind of ignored it. It then started to stall at idle. Took it to my local guy, who checked all the simple stuff: vacuum hoses, mass air flow sensor, he even removed and cleaned up the throttle body. But the problem persists.

I guess the part that really has me puzzled is the lack of a check-engine light or an error code. With how computer-regulated cars are nowadays, I’m baffled as to how this isn’t causing some alarm to go off.


Are you sure that the Check Engine Light is working?

Turn the ignition key to the “on” position, prior to engaging the starter, and make sure that the light actually works. I mention this because some unscrupulous people selling used cars have been known to remove the light bulb. So, if you bought this as a used car, it is worthwhile to make sure that the light actually works.

In any event, if your mechanic did not check the Idle Air Control (IAC), he may have missed the most significant part of the problem.

Both good ideas…but

The light was one of my mechanic’s first thoughts. It does work.
the car has belonged to one member of my family or another since it was new, and has been well looked after.
The 06 XT has Fly by wire throttle control, and does not have an IAC valve.

Should also mention, I have a code-reader and have confirmed that no error codes are popping up

just an update. my local mechanic was out of ideas, so to the subaru dealer it is! so far, they have done a vacuum test on the engine and found the compression to be a bit low on 3 of 4 cylinders. Could mean a new head gasket (ouch!) or could be nothing serious… They are continuing tests… will let you all know what the verdict is.

going on day 5 at the subie dealer. they seem properly baffled, but also aren’t charging me an arm and a leg for all this diagnostic time.

Dealer finally sorted it out. When my local guy did a routine tune-up a few months ago, they put in the wrong spark plugs. This engine requires Iridium plugs, and they put in platinum…
I’ll be paying them a visit very soon to discuss

I’m surprised that the metal type made that much of a difference (assuming they were otherwise the correct specifications - gap, etc.), but if it fixed it, then that’s good news.

I’m not a mechanic, though, so perhaps someone with more expertise than me will come along and explain why.

This is a good example of why it’s important to use only the plugs called for in the owner’s manual or service manual.

Sometimes being cheap will actually cost you more money in the end.

p.s. I meant no offense. I’m just saying that this should be a lesson to anyone reading this.

Platinum plugs are cheaper than iridium, therefore I mentioned being cheap.