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2003 Dodge Ram 2500 5.7L P0172 Rich Condition: No Idle, Throttle Required, Fix with Vacuum Leak Diagnosis

Model: 2003 Dodge Ram 2500 Fault Code: P0172 Posted: 2009-10-23 16:11

Hi everyone! I'm currently troubleshooting a 2003 Dodge Ram 2500 with a 5.7L V8 engine that exhibits a no-idle condition. The vehicle only starts when the throttle is pushed halfway to three-quarters open. A DRB3 scan revealed code P0172, indicating a rich fuel mixture. Key details: - No EGR or MAF sensor present on this model - Fuel pressure at key-on engine-off: 47 psi (holding steady) - Running at 1200 rpm: 49–50 psi - Replaced throttle body, both O2 sensors, and all fuel injectors with new parts - MAP sensor readings are normal; air charge temperature sensor appears functional Despite these replacements, the issue persists. The engine runs only when the throttle is partially depressed, and plugs show signs of a rich condition—though not fully soaked. I'm seeking advice on potential root causes beyond standard fuel system components. Any insights into possible vacuum leaks, intake manifold issues, or software-related factors would be greatly appreciated! Thanks, Mike from Michigan

Related fault codes

P0172

Comments (6)

Anonymous 2009-10-23 20:02

What are the fuel trims showing when you get it started, Mike? Is this an electronic throttle body? Have you tried disconnecting the exhaust to rule out a restriction? Are the spark plugs soaked in fuel? Where did you source your O2 sensors from?

Anonymous 2009-10-24 07:42

Hi Jeff! I'm not familiar with 'fuel trims'—could you explain what they are? The throttle body is electronic and not serviceable. I haven't disconnected the exhaust due to concerns about top-end performance; it doesn't behave like a plug-cat issue. When I inspected the plugs, all showed signs of rich mixture but weren't fully soaked. The O2 sensors are Mopar originals. I was planning to check the timing this morning just in case. Thanks for your help, Jeff! Mike

Anonymous 2009-10-24 08:48

Are you absolutely sure there's no EGR valve on this truck? If you have access to a DRB3, it should show up during actuator testing. If the DRB3 is still available, try running the engine at 2500 RPM and monitor fuel trims—this can help identify underlying issues. Another common issue with these trucks is a split intake manifold gasket causing significant vacuum leaks. With an electronic throttle body, even small leaks can cause severe idle problems. It's relatively easy to inspect and repair. Some 2003 Ram models had software updates that addressed fuel trim codes—these might keep the check engine light on without affecting performance. If you're diagnosing fuel trims, it’s essential to understand how they work and monitor them via a scan tool. Hope this helps—let me know what you find! Jeff

Anonymous 2009-10-24 14:47

Hi Jeff! After using carb cleaner to check for vacuum leaks around the intake manifold, I found a leak at injector port #7. Removed the intake manifold and confirmed that one of the injector seats had melted or burned through. Do you know if it's possible to post pictures on this site for educational purposes? Thanks again for your input! Mike

Anonymous 2009-10-24 15:14

Congrats on finding the root cause, Mike! I'm not sure about posting images—webmaster Kelly would have the final say. Do you have any idea what caused the melting or burning of the intake port?

Anonymous 2009-10-25 19:00

Hi Jeff! I’m still unsure about the exact cause—the damage looks more like a chemical burn than overheating. I work at Chrysler headquarters—I’ll reach out to the release engineer to see if they can provide insight into what might have caused this. I'll update you once I get any information! Thanks again, Mike!