Idle Air Control Underspeed Error (Ford)
What does P1507 mean?
The P1507 code means the vehicle's onboard diagnostic system has detected: Idle Air Control Underspeed Error (Ford). This is a moderate severity code.
Common Symptoms
- Engine idle speed too low (below 500 RPM)
- Check Engine Light illuminated
- Engine stalls at idle or when stopping
- Rough or shaky idle
- Engine dies when shifting into gear
Probable Causes (Ranked by Likelihood)
- Clogged or stuck-closed IAC valve Very High
- Carbon buildup in IAC passages restricting airflow High
- Restricted air intake or dirty air filter Moderate
- Low fuel pressure from a weak fuel pump Moderate
- Engine mechanical issue reducing compression Low
Step-by-Step Diagnostic Procedure
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Remove and clean the IAC valve with throttle body cleaner. Inspect for free pintle movement.
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Clean the IAC air passages in the throttle body with carburetor cleaner and a small brush.
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Check the air filter for restriction and replace if excessively dirty.
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Test fuel pressure at the fuel rail. It should be within the manufacturer specification.
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If cleaning does not help, replace the IAC valve and retest.
Frequently Asked Questions
Why does my engine stall when I stop?
The IAC valve is not allowing enough bypass air to maintain idle speed. When additional loads are applied (AC, power steering at full lock, automatic transmission in gear), the engine cannot maintain idle and stalls.
Can a dirty air filter cause low idle?
A severely restricted air filter can reduce airflow enough to affect idle speed, though this is less common than IAC valve issues. Check the filter as part of your diagnosis.
How often should the IAC valve be cleaned?
There is no set interval, but cleaning the IAC valve and throttle body every 30,000 to 50,000 miles as preventive maintenance can avoid idle problems on Ford vehicles.