P1512: Idle Speed Below Target
The P1512 code indicates that the Powertrain Control Module (PCM) has detected the engine idle speed is lower than the desired operating range, even though the idle air control (IAC) actuator is commanded fully open. The IAC system regulates bypass air around the throttle plate to maintain stable idle RPM. The PCM monitors engine speed via the crankshaft position (CKP) sensor and compares actual RPM to the target. When the PCM cannot achieve the programmed idle speed with the IAC at maximum, it sets this diagnostic trouble code. In Ford vehicles, this code is often linked to a faulty IAC solenoid, restricted air passages, or engine mechanical issues preventing proper idle.
01. Most Common Causes
- Faulty IAC solenoid/actuator (open coil, short circuit, or mechanical wear)
- Carbon buildup blocking the IAC bypass air passage
- Vacuum leak in the intake manifold or connected hoses
- Dirty or sticking throttle valve restricting minimum air flow
- Faulty throttle position (TP) sensor sending incorrect signal
- Engine mechanical problems (low compression, incorrect timing)
- IAC circuit wiring issues (short to ground or open circuit)
- Failed PCM (rare)
02. Symptoms You Will Notice
- Rough or low idle (engine may stall)
- Check Engine Light illuminated
03. Step-by-Step Diagnosis
Scan for codes and verify P1512 is present.
Inspect IAC actuator and wiring for damage or corrosion.
Check for vacuum leaks using a smoke machine or propane enrichment.
Clean throttle body and IAC air passage with approved cleaner.
Test IAC solenoid resistance and compare to specifications.
Monitor TP sensor voltage and idle RPM with a scan tool.
Perform a compression test and check timing if mechanical issues are suspected.
1. Frequently Asked Questions
Is it safe to drive?▼
You can drive short distances, but the vehicle may idle poorly or stall, especially when coming to a stop. It's best to have it diagnosed and repaired promptly to avoid further issues.
How much does it cost to fix?▼
Repair costs typically range from $100 to $400, depending on the cause. Cleaning the throttle body or IAC passage may cost under $100, while replacing the IAC actuator or TP sensor can be $150-$300. Major engine repairs would be more.