Subaru mystery

I’m looking for any ideas people have to help solve my Subaru mystery. I have a 2008 Outback and despite the efforts of two different shops and almost three years, no one can figure out how to fix my car. Within the first 5 to 10 minutes of driving, if you come to a stop (or just get below about 1000 rpms,) the car will die. If you try to restart it right away, all the lights will come on and it will turn over and sometimes catch for a few seconds but will die even if you rev the engine. If you wait for 3 to 10 minutes and try again, so far it has restarted and then been fine for the remainder of the trip. The problem is it does not happen every day–it’s totally random so of course it doesn’t happen for the repair guys. It’s just had its 60,000 mile service, so has all new plugs, wires, fluids, etc and is still misbehaving. It never throws a code when it has these episodes, so makes it even harder to diagnose. The shops think I’m crazy. Any one have and ideas or advice? Thanks!

There is nothing like a good Subaru mystery. We love to solve them.

From what you say about the problem I would suspect something with the fuel delivery system is causing the trouble. It could be the fuel pump itself, the relay for it, or a power wire connection to those things. Always start with the simple things first, like the wiring and relay. To verify this is a fuel issue you could try spraying a small amount of starter fluid into the intake to see how the engine reacts to that when the trouble happens again. Carry the can in the car with you. If it runs for a bit using that then you need to check the fuel system since the ignition system appears to be okay using that test.

You will need to buy or borrow a code reader and keep it in the car. You may be getting a type 2 (or B) DTC which will not trigger the check engine light on the first occurrence and will disappear if the next drive cycle is clean.

When this happens, you will need to immediately pull the code(s), they will show up as a pending code.

Will the engine die if you do not come to a stop or drop below 1000 rpm? You say it happens only under these two conditions. If that’s true it sounds like a flaky idle air control valve. You could try replacing the idle air control valve and see if that helps.

I don’t think it could be a fuel pump/fuel delivery issue because the stalling is happening only at stop/low idle conditions. A fuel delivery issue issue would cause stalling even at higher engine rpms, not just idle.

I agree with @jesmed, the idle air control valve is a more likely trouble spot than my original thought of the fuel system as the cause of the trouble. Just cleaning it along with the MAF sensor may fix this trouble. Other things that may help are changing the PCV valve and fuel filter if those haven’t been done already.

Wouldn’t an IAC problem that bad throw an IAC code? The ECM should measure the idle speed, so if it commands the IAC to a certain idle speed, and it didn’t get that measurement, you’d think it would know that there was an IAC control problem and throw a code.

OP: You need to be able to narrow this down between the three most likely culprits.

  • IAC
  • Fuel pressure
  • Spark

Ask your shop if they can instruct you and provide you the necessary test equipment to take with you to differentiate between these three next time it happens. If not, your best bet is probably to simply loan this car to the shop for however long it takes. Tell them that one of their staff techs can drive it as their daily driver. Eventually the problem will happen and then the staff tech driving the car can find out which of the above three is the problem.

“Within the first 5 to 10 minutes of driving…”

Makes me suspect the engine coolant temperature sensor and connector.

I thought about the coolant sensor also as a possibility. That could be monitored on the OBD2 port.