Subaru Impreza turns over but won't start intermittently

Subaru Impreza 2004 2.5 TS
170,000 km

For a couple of months now and every few days, my car turns over nicely but chokes. I can keep the engine running by pressing the gas pedal as lightly as possible without letting the engine stop or rev too high, and after about 15 seconds it stays on on its own. When it’s running it runs very smoothly…no knocking or shuddering or poor idling at lights.

So there’s obviously a gas delivery problem at startup. I don’t know if I can but I would love to rule out the fuel pump since it’s only at startup (fuel filter is new, battery is new, and sensors have been checked, even during a failure to start scenario) and it runs so well when driving. Also, it won’t start randomly, regardless of temperature, cold start or not, incline, etc. I read that a fuse can have intermittent problems but again it seems to me that it should be properly intermittent, not just at startup. Which leaves the relay and wires.

Now thinking about wiring, a few years ago I noticed I could no longer leave my highbeams on. I could hold the lever and make them stay on, but pushing the lever into the on position no longer works. Also, recently and only once, on a -26 C day, the air compressor was dead when I started the car. After stopping and starting for a half an hour I noticed thankfully that it had come back on. Does this sound like it could be connected? Where do I even start to diagnose this starting problem?

I appreciate any hints anyone might come up with because I adore this car and in so many ways it’s premature to replace it.


What is the “air compressor”?

Sounds like several unconnected problems. First, check fuel pressure when start-up problem occurs.

You need to check the fuel pressure and make sure it’s maintaining some residual pressure while the car is sitting. If pressure is being lost the cause in most cases is the check valve in the fuel pump.

The rough running is air being purged out of the fuel lines when started. As an analogy, think of a garden hose when first turned on and the spitting and sputtering that occurs until the air in the hose is belched out. The same thing occurs with fuel lines if gasoline is bleeding off.