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P1506 Fault on 1996 Mazda 626: Causes, Diagnostics & Cost-Saving Fixes

Model: Mazda 626 Fault Code: P1506 Posted: 2005-02-27 19:36

Hi there, I'm dealing with a recurring P1506 fault on my daughter's 1996 Mazda 626. The car runs smoothly otherwise, but the idle speed is consistently high at around 800 RPM. I've already cleaned both the Mass Air Flow (MAF) sensor and throttle body, replaced the ECT sensor, and disassembled the Idle Air Control (IAC) valve — which appeared clean during inspection. No vacuum leaks were detected. Prior to these repairs, I was experiencing P0171 (rich mixture) and a misfire code, both of which have since resolved. Now only P1506 remains. This has led me to suspect an issue with the idle control system or engine management module. I'm looking for reliable diagnostics: Is the IAC valve faulty? Could there be a wiring issue or short in the Engine Control Module (PCM)? What about intake gasket leaks or coolant sensor inaccuracies that might cause erratic idling? Any real-world fixes, especially cost-effective ones, would be greatly appreciated — I'm trying to avoid spending over $400 on a replacement IAC valve if it's not truly necessary.

Related fault codes

P1506

Comments (6)

Anonymous 2005-02-27 21:40

P1506 indicates an Idle Air Control (IAC) System Overspeed Error. While I don't have direct experience with this code on the Mazda 626, it's worth checking a manufacturer-specific repair manual or considering replacing the IAC valve as a next step.

Anonymous 2005-02-28 19:15

I considered replacing the IAC valve due to its high cost — over $400 including parts and labor. Before proceeding, I want to be certain it's actually faulty. The P1506 code appeared after I cleaned the throttle body in an attempt to fix a prior P0171 issue. Since then, that code has not returned. This suggests the problem may lie in the throttle plate not closing fully — possibly due to mechanical obstruction or wear.

Anonymous 2006-01-21 21:26

IAC valves often cost over $400 and require special O-rings and gaskets for proper installation, making them a costly fix that may not be the root cause. You've already checked for vacuum leaks — next, inspect your PCV valve. The resistance between IAC solenoid pins should fall within 7.7 to 9.3 ohms; if outside this range, the valve is likely defective. A short to ground in the PCM could also be causing the issue. If you disconnect the IAC connector after engine warm-up and the idle remains high (or doesn't drop), it may indicate a wiring fault or faulty PCM. The earlier misfire code was probably caused by carb cleaner use or intake cleaning — temporary debris removal. This is a tricky diagnosis, so proceed cautiously to avoid unnecessary expenses. Please share your findings if you test any of these steps.

Anonymous 2006-01-25 10:27

I've seen similar idle issues on Mazda 626 models and suspect intake gasket leaks near the front of the engine block, especially on the passenger side. These leaks can cause vacuum loss and result in erratic idling. Also check coolant levels — if low or if the coolant sensor is inaccurate, it may trigger surge conditions that raise idle speed significantly. I recall a Mazda Technical Service Bulletin (TSB) addressing this issue; contacting Mazda directly might yield helpful guidance. Good luck — feel free to update this thread if you find a solution.

Anonymous 2006-02-08 22:04

This thread is quite old, but I wanted to share my experience with a 1998 Mazda 626 that showed P1506 and P0420 codes. The IAC valve replacement cost over $400 — a significant investment. Instead, I purchased a used throttle body for $75 and a new gasket for $2.50. The swap took just 15 minutes, and after reassembly, the check engine light turned off and idle stabilized — the car now runs smoothly like a kitten. This suggests that intake-related components may be more cost-effective than full IAC replacements.

Anonymous 2006-03-15 21:43

Just to add: There are known technical service bulletins (TSBs) for the 1996 Mazda 626 related to idle control issues. These documents may provide specific guidance on diagnosing and repairing P1506 — worth reviewing if you're looking for official Mazda recommendations.