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1996 Jeep Grand Cherokee P0505 Code: Idle Control System Malfunction and Engine Dies in Gear

Model: 1996 Jeep Grand Cherokee Fault Code: P0505 Posted: 2006-07-28 09:32

I'm experiencing a recurring issue with my 1996 Jeep Grand Cherokee (4.0L I-6, Country model). The vehicle starts fine but dies immediately when shifted into gear. The check engine light is triggered by code P0505 — Idle Control System Malfunction. After replacing the Idle Air Control (IAC) valve, the car ran smoothly for about 6 hours before the MIL began acting erratically and the problem returned. I suspect the issue may lie with the Single Board Engine Controller (SBECii), as it's responsible for managing idle air flow. The vehicle idles at a slightly high RPM but does not surge. When I press the accelerator, there is a noticeable delay before response. I've checked the throttle body and believe the internal throttle screw may have been adjusted improperly — this could affect minimum airflow settings. I'm also wondering if an aftermarket IAC valve was installed incorrectly or isn as calibrated for my engine. I'd like to know: Is the idle surging? Does it idle at all? What happens when the vacuum hose connected to the EGR valve is disconnected? Can a scanner that can command the IAC pintle and show step positions of the motor help diagnose this? Any insights or troubleshooting steps for P0505 on a 1996 Jeep Grand Cherokee would be greatly appreciated.

Related fault codes
P0505
Comments (3)
Anonymous 2006-07-28 09:58

A noid light can help verify whether the IAC valve is being commanded by the PCM. Aftermarket IAC valves may not be properly calibrated, especially if they were installed without following manufacturer specifications. If the throttle screw in the IAC valve body has been adjusted, it could cause incorrect minimum airflow — this needs to be reset. A scanner capable of commanding the IAC motor and displaying step positions is essential for accurate diagnosis. Does your vehicle idle smoothly? Is there any surging or hesitation when idling?

Anonymous 2006-07-28 10:20

The IAC valve packaging notes that at normal engine temperature and a road speed of 40 MPH, the PCM should command the pintle to reset. The vehicle does idle, though slightly high. There's also a noticeable lag when pressing the accelerator — it seems to 'hang' for a few seconds before responding. I'm unsure what happens if the vacuum hose to the EGR valve is disconnected; any experience with that test?

Anonymous 2006-07-28 12:04

Is this an original Mopar part or aftermarket? Has anyone adjusted the throttle screw in the IAC valve body? If so, that could have disrupted airflow calibration. Also, please confirm if the engine timing is correct and whether there are any vacuum leaks. Is the idle behavior stable or does it surge under load?