2002 Ford Taurus P1504 Code: Idle Control Valve Replacement Not Resolving Issue

Check if the idle is stable and being properly controlled by the Powertrain Control Module (PCM). If the idle is steady, try disconnecting the voltage regulator from the alternator while the engine is running. If the P1504 code clears, it may indicate an electrical interference issue. If the code remains, inspect the diode pattern on the B+ terminal of the alternator with the engine running and electrical loads (like headlights or blower motor) engaged. Erratic voltage spikes suggest a faulty alternator that should be replaced.

Hi, I believe you may have meant to replace the idle control valve rather than the intake air control valve. Also, avoid disconnecting the alternator or regulator while the engine is running — this can cause serious damage. It's important to clarify whether such tests are being performed with the engine off or on. First, verify that the sensor wire connector receives proper voltage supply. This basic check may help identify if there’s a power issue upstream of the P1504 code. Please keep us updated.

Hey Fuel Injection — what damage could occur if the alternator regulator is unplugged while the engine is running? The alternator would stop charging, leading to a loss of electrical power. Additionally, faulty diodes in the alternator are known to cause intermittent issues and should be considered as a potential root cause.

Hi asecmt! I agree that diode failure in alternators can lead to problems. However, I’m unsure how this directly relates to P1504. There may be more effective diagnostic methods than disconnecting the alternator or regulator. Still, if such tests have worked for you in similar cases, it would be valuable to share your experience. By the way, unplugging the regulator while the engine is running could cause sudden voltage spikes — potentially damaging the alternator or electrical systems. While this isn’t guaranteed, it’s a real risk and should be approached with caution. If you’re 90% confident no damage occurs, please explain why. Thanks for your input — this helps improve our understanding and troubleshooting skills. Keep posted!

Actually, disconnecting the alternator regulator is a recognized diagnostic method used by professionals to test for electrical interference from the alternator. I’ve personally been advised to perform this step by specialists. So I agree with asecmt — it can be an effective way to isolate alternator-related issues.

Thanks, darkrooms! I've had multiple alternator replacements on Ford vehicles due to P0340 (a different code), and I know that alternator electrical interference can cause various problems. While this may not be the root of your P1504 issue, it's worth considering — especially since alternators are often overlooked when diagnosing charging system faults. Before proceeding with any tests, confirm whether the idle control valve is actually functioning properly via a KOER (On-Board Diagnostics) self-test. This would provide clearer diagnostic insight.

Thanks again, asecmt and darkrooms! I didn’t know about this alternator interference test you're describing — and it's reassuring to hear that such tests don't necessarily cause damage. That’s an important point for safe diagnostics. This discussion is helping me better understand the troubleshooting process and improves my confidence in handling similar issues in the future. Keep sharing insights!