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P0507 Fault on 2002 GM 5.3L Engine: Diagnosis and Solutions for Idle RPM Issues

Model: GM 5.3 Fault Code: P0507 Posted: 2012-10-10 10:08

I own a 2002 GM 5.3L V8 engine that is triggering a P0507 diagnostic code. The idle RPM consistently stays around 625, rarely exceeding 650. I've already inspected the PCV valve and confirmed it's functioning properly. The throttle body is manual, and the EGR valve has been removed (transplanted into a 1970 Toyota FJ40) to avoid smog compliance issues. The engine was running smoothly for approximately 2,000 miles after installation before this code began appearing. After clearing the P0507 code, I typically drive 100–200 miles before it returns—most often during freeway driving, which suggests it's not directly related to idle RPM. I've conducted vacuum leak tests using both starting fluid and an unlit propane torch, with no noticeable increase in engine speed as recorded by my scan tool. When introducing the fluids into an open vacuum line, there was no detectable change in RPM. I have also cleaned the Idle Air Control (IAC) module, and IAC valve resistance readings are within normal range. The IAC count during operation is between 35 and 45. No other diagnostic trouble codes (DTCs) are present. Freeze frame data shows that the code was set when RPM reached 1,100. I've consulted a local shop who performed a smoke leak test on a cold engine—identifying a minor vacuum leak at the EGR port in the intake manifold. After resealing and checking, the issue returned within 20 miles of driving. The code remained pending after another 5-mile drive at home. I'm now considering whether modifications to the engine or electrical components (such as TPS or voltage issues) could be causing the PCM to misread RPM. Additionally, I've noticed that during gear shifts with a manual transmission, the engine sometimes takes longer than usual to drop RPM when throttle is released. This behavior may be related but remains unconfirmed. Any insights into possible causes of P0507 on this specific 2002 GM 5.3L setup? I'm open to suggestions involving PCM calibration, vacuum integrity, or sensor-related issues.

Related fault codes

P0507

Comments (4)

Anonymous 2012-10-10 10:36

Did you remove or disable the EGR valve on this engine? Or is it not present at all? Your scan tool supports manufacturer-specific codes (P1xxx)? I suspect P1441 might be involved. Note: The P0507 code triggers when actual RPM exceeds the commanded RPM by 200 rpm. Could you please share all active DTCs? Also, try commanding your scanner to set RPM to 1500—what happens? Please provide freeze frame data so we can analyze the exact conditions under which the code was triggered.

Anonymous 2012-10-10 12:08

My scan tool is not manufacturer-specific. I'll try to obtain P1xxx codes from another diagnostic device. The EGR valve was removed due to the non-smog compliance requirement of the 1970 Toyota FJ40 chassis. The PCM has been reprogrammed accordingly. By the way, the engine ran smoothly for about 2,000 miles before this P0507 code appeared. Additionally, after clearing the code, it returns during highway driving after 100–200 miles—this strongly suggests it's not an idle RPM issue.

Anonymous 2012-10-10 13:02

Engine modifications should be considered as a potential factor. Why did this issue appear only now and after 2,000 miles of operation? And why does it return after just 200 miles of driving? Could there be voltage fluctuations or a throttle position sensor (TPS) fault causing the Powertrain Control Module (PCM) to misinterpret RPM readings?

Anonymous 2012-10-18 09:39

I had a professional scan and diagnosis performed. The IAC module showed counts between 35 and 45, with normal resistance across its pins. No other DTCs were detected. Freeze frame data indicates the code was triggered at an RPM of 1,100. A smoke leak test conducted on a cold engine revealed a minor vacuum leak at the EGR port in the manifold. The technician resealed it and inspected the area. However, within 20 miles of driving, the P0507 code returned. After resetting, the code became pending after just 5 miles at home. I'm planning to return for further diagnosis—perhaps it's time to consider replacing components. One additional symptom: during manual gear shifts, RPM drops slowly when throttle is released.