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P1506 OBD2 Code Diagnosis and Idle Issues in 2003 Mercury Sable

Model: 2003 Mercury Sable Fault Code: P1506 Posted: 2014-02-17 15:13

I'm new to this forum, but I'm experiencing a persistent issue with my 2003 Mercury Sable. After using an OBD2 scanner, I received a P1506 code, which prompted me to replace the Idle Air Control (IAC) valve. However, after installation, the engine now idles between 2500 and 3000 RPM—significantly higher than normal—and the idle speed fluctuates rather than stabilizing. The service engine light was not on during this period, which is unusual. I initially assumed that replacing the IAC valve would resolve the issue, but instead, it appears to have worsened the problem. After cleaning and re-installing the original IAC valve, the idle stabilized and the engine light turned off. This led me to suspect that using a non-Motorcraft IAC valve might be the root cause, as Ford has issued technical notes advising against aftermarket parts in this model. I'm now wondering whether I should continue with further repairs or simply accept the current behavior. Could the issue stem from an incorrect idle adjustment or a vacuum leak? Any insights into how to properly diagnose and fix this P1506-related idle problem would be greatly appreciated.

Related fault codes
P1506
Comments (6)
Anonymous 2014-02-17 22:03

What is your IAC percentage reading on the scan tool? Please share idle RPM, desired RPM, and TPS voltage for a more accurate diagnosis.

Anonymous 2014-02-18 09:56

I previously thought I had a scanner—actually, I have a 3030 Innova OBD2 reader. It's simple to use and cost-effective, especially since I'm a woman and wanted to avoid being taken for a ride at a garage. The device detected P1506. After replacing the IAC valve with a new one, idle RPM jumped to 2500–3000 and fluctuated. When we cleaned and reinstalled the original IAC, idle stabilized and the service light turned off. I read a Ford technical note warning against using non-Motorcraft parts—could that have been the issue? Should I consider leaving it as is or try further repairs?

Anonymous 2014-02-18 17:37

An aftermarket IAC valve was likely the problem. I've seen this P1506 code before when users attempt to lower idle RPM by adjusting the idle stop screw.

Anonymous 2014-02-19 12:10

Thanks—this makes sense. I'll probably have to wait and see if any new codes appear in the future, especially after a reset or further inspection.

Anonymous 2014-02-24 14:39

I replaced the IAC valve with an authentic Motorcraft unit (cost nearly double). The idle remains high and the engine light stays on. Help! I've read that replacing the bushing inside the IMRC valve might fix this issue—how can one locate and access it?

Anonymous 2014-02-24 19:02

Gened wrote: I replaced the IAC with a Motorcraft unit (cost nearly double). Idle remains high and engine light stays on. Help! I've read that replacing the bushing in the IMRC valve might fix this issue—how can one locate it? I'm not an expert, but online sources suggest that even after installing a correct IAC valve, a reset of the ECU is required to clear old idle data from the previous valve. This reset may be necessary for proper operation. We tried it and it didn't help. That's why I posted this question. Other suggestions point toward possible vacuum leaks—perhaps that’s worth investigating as well. Hope you find a solution!