What P0505 means
At idle, a small computer-controlled valve (or throttle motor on newer cars) meters exactly the air the engine needs to run unloaded. P0505 means idle speed won't obey — the control system commands and the engine idles wherever it can, which is where stalling and racing idle both come from.
What you’ll notice
- Stalling at stops or on startup
- Idle too high, too low, or hunting up and down
- Stumble when A/C or steering load hits
- Check engine light
Likely causes and repair cost
Broad US independent-shop bands, parts and labour.
Can you drive with P0505?
With stalling caveats — an engine that dies at stops takes power assist with it at bad moments. Book it promptly; the fix is often just a cleaning.
The misdiagnosis to avoid
Skipping the relearn. Many cars need an idle relearn procedure after cleaning or replacement — battery-disconnect rituals or scan-tool routines — and without it the 'fixed' car idles badly out of the gate, parts get blamed, and a second round of spending starts. Ask specifically whether yours needs one.
How P0505 actually gets set
The engine computer continuously compares what its sensors report against what its model of the engine expects. When a reading stays outside the expected window long enough to rule out noise, it stores a code and, if the fault affects emissions, illuminates the check engine light.
What a scan tool shows that the code does not
Freeze-frame data — the snapshot of engine speed, load, coolant temperature and fuel trim captured at the moment the code set. Those conditions frequently identify the cause faster than the code description does, because they tell you what the engine was actually doing when it failed.
The trap with this family of codes
Treating the code as a part number. A diagnostic trouble code names a circuit or a condition the computer observed, not the component that needs replacing. The gap between those two things is where most unnecessary parts spending happens.
What happens when you clear it
Clearing a code also resets the emissions readiness monitors, which inspection stations check. Arriving at a test with incomplete monitors fails just as surely as arriving with the light on, so fix the cause and let the system verify itself over several days of normal driving.
A steady light with no change in how the car drives means read the code within days. A flashing light, or any new symptom alongside the code, raises it immediately.
Describe what it’s doing in your own words and the symptom checker gives you a safe-to-drive verdict, ranked causes with costs, and notes to take to the shop — free, no sign-up.
A basic code reader costs around $25 and usually pays for itself the first time a warning light comes on. We compare them in choosing an OBD2 scanner.
Questions people ask
Why does it stall only when I turn the steering at parking speed?
Power steering load at idle is the heaviest sudden demand the idle system faces — the pump loads the engine and the idle control must instantly add air. A fouled valve adds it late, and the engine dips or dies precisely during parking maneuvers. That symptom is nearly a component name.
The idle races high instead — same system?
Same system, opposite failure: a valve stuck open (or a vacuum leak it can't close against) feeds too much idle air. High idle is less stall-prone but harder on the transmission at engagement and worth the same cleaning-first approach.