- Joined
- Jul 2, 2007
- Messages
- 5,293
After an exhaustive several months of chasing an intermittent idle quality problem that would also extend into slight driveability issue during warm-up. The whole thing mimicked a vacuum leak but never found any. Even went so far as to replace PCV valve in case it was the cause although it rattled around just fine like they're supposed to. Considered it to be possible flaky brake booster but it passed the usual test to reveal a bad booster and brakes never felt excessively hard or spongy.
Well I finally nailed it. It was the reference air hose for the fuel tank pressure sensor. It was jammed up and not sampling atmospheric pressure properly. Never tripped a CEL, although it would seem it would be prone to, due to being in the evap emissions suite of sensors. Once I freed it and corrected it, everything is back to normal and she's running great again. Idle is smooth again, low end torque is back where it should be, and warm-up behavior is back to normal.
As far as I can tell the lack of proper reference pressure to compare against in-tank pressure was causing it to run a pressure check cycle when it wasn't optimal and more often than normal. Only a theory, but there is no denying that since I resolved the hose issue the car driveability issues are gone. It is not a vacuum hose although it is the same size and type, just no vac sucking through it, it is there to provide a reference air pressure source for the fuel tank pressure sensor and ECU to calculate fuel tank pressure against atmospheric pressure of the environment around the car.
Pretty obscure problem, glad I found it.
Well I finally nailed it. It was the reference air hose for the fuel tank pressure sensor. It was jammed up and not sampling atmospheric pressure properly. Never tripped a CEL, although it would seem it would be prone to, due to being in the evap emissions suite of sensors. Once I freed it and corrected it, everything is back to normal and she's running great again. Idle is smooth again, low end torque is back where it should be, and warm-up behavior is back to normal.
As far as I can tell the lack of proper reference pressure to compare against in-tank pressure was causing it to run a pressure check cycle when it wasn't optimal and more often than normal. Only a theory, but there is no denying that since I resolved the hose issue the car driveability issues are gone. It is not a vacuum hose although it is the same size and type, just no vac sucking through it, it is there to provide a reference air pressure source for the fuel tank pressure sensor and ECU to calculate fuel tank pressure against atmospheric pressure of the environment around the car.
Pretty obscure problem, glad I found it.
