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2003 GMC Yukon XL 5.3L P0300 Code: Rough Idle at Idle, No Other DTCs After Air Filter Change

Model: 2003 Yukon Fault Code: P0300 Posted: 2018-02-03 16:24

This issue is driving me insane. I only start seeing the P0300 code when the engine is idling. I can drive long distances—up to 43 miles each way on highway—with no problems. I've already replaced the intake manifold gasket, MAP sensor, all spark plugs, plug wires, and coil packs. Despite these repairs, the P0300 code persists. Here's my Freeze Frame data: - DTCFRZF: P0300 - Fuelsys1: OL (Open Loop) - Fuelsys2: OL? (Open Loop) - Load_pct%: 3.9% - ect: 170°F - shrtft1: -7.8 - longft1: 3.1 - shrtft2: -9.4 - longft2: 4.7? - map: 41.0 kPa - rpm: 722 - vss: 0 - maf: 9.89 g/s - tp: 11.0 psi All spark plugs appear identical in condition. Initially, I received a MAF sensor error and cleaned it with MAF cleaner. No other diagnostic codes are present. This is a 2003 GMC Yukon XL 5.3L V8 (non-fleet) with 145,000 miles. Any insights or troubleshooting steps would be greatly appreciated.

Related fault codes
P0300
Comments (7)
Anonymous 2018-02-04 11:05

The fuel system is in open loop mode. Ensure the engine reaches operating temperature (around 210°F) — avoid lowering the thermostat rating. Use a proper paper air filter, not an oil-impregnated type. Add a can of SeaFoam or Techron fuel system cleaner. Drive for several miles with the cleaner in the tank, then post the system status to 'Closed Loop'. Confirm you're using AC Delco spark plugs. Perform a fuel pressure test and observe the drop under KOEO conditions — note any drop over 5 minutes (e.g., 10 psi).

Anonymous 2018-02-04 16:30

I currently use a K&N air filter, installed over 75,000 miles. I also switched to AC Delco plugs as recommended. I drove around the block and reached 195°F. Next step is adding SeaFoam and performing a fuel pressure test — will update with results tomorrow.

Anonymous 2018-02-06 17:49

Still haven't had time to get a fuel pressure gauge yet.

Anonymous 2018-02-08 20:24

I tested the fuel pressure: 25 PSI when key is on, and 40 PSI while running. This suggests a possible fuel pump issue.

Anonymous 2018-02-09 09:09

The pressure seems low — verify against OEM specifications. A thought: test fuel pressure with the engine off (KOEO) and observe any drop over 5 minutes. If it drops more than 10 PSI in five minutes, check for fuel in the engine oil and inspect spark plugs for wet or black fouling.

Anonymous 2018-02-17 15:00

I ordered a new fuel pump. While waiting, the Yukon ran perfectly for an entire week. Then on Friday, it started acting up again. I'm currently replacing the fuel pump and will post results shortly.

Anonymous 2018-03-04 20:41

Not to keep you all hanging — due to rain and delays, I finally received the fuel pump. It helped slightly, but after someone asked about my air filter type, I replaced it with a standard paper filter out of desperation. The P0300 code disappeared and the rough idle stopped. Now over a week later, everything has remained stable.