2001 Subaru Outback throttle position sensor

  • 2.3L
  • 4 CYL
  • AWD
  • 92,000 MILES
Runs OK when first started. After engine warms (before even leaving driveway) and travels about 1 mile it starts acting like it is starving for gas and wants to stall. I have been able to limp it home by feathering the gas but just barely. Put 1 container of ignition cleaner in and thought problem was solved for about 50 - 100 miles.. Not. The car has charged ahead and increased speed without touching the gas. I brake and put it in neutral, rev the gas some and seems OK until next time. Engine check light comes on occasionally but not long enough to take it to have OBD done. Help! Please!
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have the same problem?
Friday, September 5th, 2014 AT 6:51 PM

1 Reply

The Check Engine light doesn't have to be on to read the diagnostic fault codes. There's over 2000 potential fault codes, and about half of them never turn the light on. When the Check Engine light goes off while you're driving, that indicates it's an intermittent problem and a relatively less-serious one. The fault code that triggered the light will stay in the Engine Computer's memory unless you disconnect the battery or let it run dead.

There's two common things that can cause the symptoms you described. One is a failing MAP sensor, but those were common on Chrysler products in the early '90s and it was their main fuel metering sensor. Total failure rarely took longer than a day once symptoms started, and the clue was the engine would stall when the throttle was held at a steady position. You could keep the engine running as long as the accelerator pedal was moving, regardless of position.

Chrysler is the only manufacturer that has been able to make an engine run right with just that MAP sensor. Every other manufacturer uses a mass air flow sensor too. Check the fresh air tube between that sensor and the throttle body. If there's any leak in it, air that sneaks in through it won't be measured so there won't be any fuel commanded to go with it.

The other common cause is a plugged or collapsed pickup screen inside the gas tank. Once the engine stalls, the screen usually stretches out again after a few minutes, and the engine will run okay for two to five miles. If you have a fuel pressure gauge and there's a test port on the fuel rail on the engine, you can clip the gauge under a wiper arm, and you'll see the fuel pressure gradually drop while you're driving. Stalling will occur when the pressure gets low enough.
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Friday, September 5th, 2014 AT 8:15 PM

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