PO300 Code Diagnosis and Fixes for 2002 Chevrolet Silverado 5.3L V8

If no other codes are present, new spark plugs—specifically AC Delco—are a good starting point. Also consider adding one can of SeaFoam for fuel injector cleaning. A fresh fuel filter is always recommended. For deeper diagnostics, get a fuel pressure gauge from your local parts store (many offer rentals). Check the condition of the removed spark plugs—cracked or fouled ones may indicate underlying issues.

Thanks for the advice, Kev2. I forgot to mention that my first OBD-II code was related to an Idle Air Control (IAC) sensor—though it disappeared before I encountered the PO300. I'm planning to replace the spark plugs with AC Delco, install a new fuel filter and EGR valve, and clean the idle air control sensor as suggested. I'll also try SeaFoam and investigate fuel pressure using a gauge loaner from the parts store. Where is the fuel pressure gauge typically connected? My Silverado runs great on the highway—I just want to fix this idle/stalling issue. Thanks again!

Don’t overlook throttle body cleaner—this can improve idle stability. As for replacing the EGR valve, it's a costly part ($200+) and not typically a primary cause of PO300. The fuel rail has a dedicated port where you can attach a fuel pressure gauge. Do you have a mechanical throttle cable or drive-by-wire? This affects diagnostics.

Kev2, I’ll hold off on replacing the EGR valve and first check if it’s stuck—just a possibility based on older literature. I’m now leaning toward fuel pressure issues because after several errands today, the start time varied significantly—sometimes fast, sometimes slow—something that didn’t happen in years past. It runs smoothly at highway speeds and accelerates without hesitation, so spark-related causes seem less likely. If there’s a fuel leak, would that point to a faulty pressure regulator (located on top of the engine with vacuum hose) or could it be a worn-out fuel pump in the tank? Thanks for your insight.

You're clearly on the right track—this is likely a list of potential causes, not one single issue. Fuel pressure regulator (FPR) testing is essential: remove the vacuum hose and check for fuel leakage—any visible fuel indicates a bad FPR. However, other possibilities include injector issues or line leaks. The EGR valve reports pintle position to the PCM—if it had degraded over 10+ years, the PCM would have set a specific code, so it's low on the priority list. The fuel pump is located in the tank and typically fails only when the tank is full—this is an often-overlooked fact. A fuel pressure gauge is a must-have tool—not expensive—and highly recommended for accurate diagnosis. *Note: 'FPR' is an older term, but still widely used.*

Kev2, you've been incredibly helpful. I’ll look into getting a fuel pressure gauge and check what the normal readings should be for my 2002 Silverado. Where can I find official fuel pressure specifications? Thanks again! P.S. My son’s 2007 Cobalt is now showing PO113 and PO102—both related to MAF/IAT sensors. I plan to replace the MAF (which includes an integrated IAT sensor), but there's another factor at play. I really miss older cars—I’d rather drive my 1963½ 427 Galaxie!

Fuel Pressure Specifications: - Key On, Engine Off: 55–62 psi - Idle Condition: 45–59 psi Before replacing the MAF/IAT sensor, check all connectors and wiring for corrosion or loose connections—this is a common cause of intermittent faults.

Since you mentioned your son’s Cobalt, a quick note: MAF sensors—especially aftermarket K&N filters—are often used. However, modifications can interfere with sensor readings. As my colleague noted, frequent air filter changes may stress wiring or cause disconnections. Always ensure proper installation and secure connections.

Mohawkmtrs, thanks for the fuel pressure specs. Kev2, no modifications on the Cobalt—fully stock. Initially only PO113 (Intake Air Temperature circuit high input) appeared. After clearing the code and removing ductwork to inspect the MAF sensor, the PO113 disappeared—but now I get PO102 (Mass or Volume Air Flow low). When I clear this code, the car starts on the third attempt but idles at around 1,000 RPM when warm. The idle remains high and the PO102 code stays pending and confirmed. This behavior didn’t exist before I removed the ductwork and inspected the sensor. Additionally, after sitting in the garage for a week, the car sometimes won’t start—seems like the starter isn’t engaging. After multiple attempts, it eventually starts. Another odd symptom: when the car acts up, turning the key on runs but doesn’t start, and the fuel gauge stays at zero with messages indicating 'low fuel' and power steering failure. Once, after starting, the fuel gauge didn’t update and power steering failed—everything returned to normal after a restart. Could this indicate PCM malfunction or an electrical issue?

The fact that systems like the fuel gauge, tachometer, and power steering don't power up when the key is turned suggests an ignition switch issue—possibly not a key lock problem. A remote starter or aftermarket alarm could be the culprit (though you mentioned none are installed). Are you familiar with using a test light or digital multimeter (DVOM)? We can probe specific wires or relays to isolate the fault. Try swapping the 'run crank' relay in the underhood fuse box with a known-good one—ensure it’s clean and properly seated. This relay powers several systems and is controlled by the Body Control Module (BCM). If this fails, the car may not start at all or show intermittent power loss. The PCM is currently low on the list of suspects.

Kev2—thank you! I hadn’t considered that an ignition switch issue could explain why fuel gauge, tachometer, and power steering don’t activate when turning the key. That might also explain intermittent starter engagement. The car has no aftermarket alarm or remote starter. I do have a digital multimeter (DVOM) and should have a test light in my toolbox—haven’t used them in years but am comfortable with basic diagnostics if given clear instructions. I’ll try the relay swap when I return to Houston. Where are you located? Also, regarding the MAF sensor: if I remove it and break the glass, then reinstall and plug it back in—would that prevent the car from starting or only cause a rough idle and trigger a code?

Try swapping the 'run crank' relay under the hood—it powers several systems and is controlled by the BCM. I’ll double-check my memory and verify the wiring diagram to ensure accuracy. With no aftermarket devices, this should help isolate the issue. The car should crank and likely start—basic starting functions require fuel pressure and spark. If both are present, the vehicle should start reliably.