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Old 11-12-2011, 08:40 PM   #1
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Default subaru map sensor weirdness

My friend has a 2000 subaru legacy outback 2.5l (non turbo). One day he mentioned it sometimes hesitate (bog) when we gets on the gas and then will finally go. No codes. New knock sensor and O2 sensor didn't change the problem. I logged it and the most of the sensors look reasonable except every time it bogs the map sensor gets stuck at 30 kpa (idle/coast map reading). Even at WOT when it should read ~100. When it recovers the MAP sensor reads 100.

- I hooked up a mityvac to the sensor with the engine off and it's weird that the MAP value only changes when TPS changes. Meaning I can bring the sensor (off the engine, but still plugged into the harness) down to 0 kpa with the mityvac, but the ECU sees 100 kpa until I touch the throttle cable and it drops to 0. My GM ecu changes the moment I change the pressure.
- I also turned it on and revved it at idle and can repeat the stuck at 30 kpa problem every once in a while, but can't figure out what triggers it. Sometimes it will get stuck at another MAP value, but it's 30 most of the time.

Bad map sensor or wiring issues are my only guesses so we are probably going to replace the sensor. Any ideas?
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Old 11-21-2011, 08:35 PM   #2
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Guess we shouldn't have skipped the obvious stuff to check. Plugs look fouled with some signs of detonation. We swapped them and the problem is gone. MAP and IAT sensors check out fine with the volt meter, mity-vac, and heat gun. Now I need to figure out why the plugs are messed up. Besides checking the plugs in a few days, I guess watching the narrow band at idle and checking fuel trims is the next step to see if the ecu is trying to dump in a lot of extra fuel. The list of things that could be wrong seems endless... leaking injectors, oil leak into the cylinder, other sensors, etc.

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