Hello,
We are having a major issue with our 2014 Scion xB (Automatic, 166k miles). Has a rough idle with check engine light and code P0505 (Idle Air).
Replaced spark plugs, throttle body, vapor purge canister - no fix.
Took to a reputable Japanese Auto shop and they did the following checks; "Followed diag tree. No vacuum leaks, good fuel trim, pcv system working correctly, plugs are good, good spark, getting signal from app, no interference with fuel pedal. Reset system, cleared computer memory and did factory relearn, code still present. Last step in diagnostic tree is to replace PCM."
They said even if I replaced PCM they cant guarantee fix.
My question is; any thoughts? If I replace PCM with a known good used unit and have programmed to car is there a good chance it'll work properly?
Thanks in advance! We've ben racking our brains for weeks.
Well you better hope the mechanic you took it to actually did that stuff lol. Because if they really did replace/check ALL that stuff, then there may be a problem with the ECU itself. And from experience, the ECU almost never needs to be replaced. ECUs very rarely are the problem themselves; it's always a sensor or mechanical problem that needs fixing. I've seen soooo many people replacing the ECU for codes it throws when the physical problem hasn't been addressed/fixed. The ECU is designed to tell you whether something is wrong with the car, so replacing it with an identical one is not going to change anything unless you know FOR SURE it's not a physical problem like a sensor, throttle body, etc.
I'm not saying that it can't be the ECU (sometimes internal modules get shorted out), I'm just saying that there could be an external sensor/wiring/connection issue or a mechanical issue that needs to be addressed first. Good luck!
