2003 Chevrolet Express 3500 6.0L - P0101 Code: Rough Idle in Cold Weather, MAF Cleaning Not Resolved

I now have additional codes: P0141 and P0147, indicating lean conditions in both bank 1 and bank 2. I'm still unable to determine the root cause.

Check fuel pressure first — ensure it's within specifications. Look for vacuum leaks near the intake manifold gasket area. Inspect the MAF sensor snorkel for blockages or damage. Also verify that the MAF is clean and providing accurate readings. Don't forget to check the EGR system for faults.

Jeff, Thank you for your response. Here's a snapshot of my vehicle’s data list: AB SLT TPS: 0.0 CALC LOAD: 1.2 COOLANT TEMP: 183°F RPM: 548–572 FUEL SYS 1 & 2: CLOSED IAT: 25–27°C IGN ADV: 12–16° LT FL TRM 1: 25.00% LT FL TRM 2: 25.00% MAF: 0.43 g/s MAP: 11.5 psi OBD STATUS: OBD1 O2S BNK 1 %: 1.96–2.35% O2S BNK 1 V: 0.025–0.030V O2S BNK 2 %: 6.27–6.67% O2S BNK 2 V: 0.080V O2S BNK 2 #1 V: 0.020–0.025V O2S BNK 2 %1: 1.57–1.96% O2S BNK 2 #2 %: 6.27% O2S BNK 2 #2 V: 0.080–0.090V ST FL TRM 1: 51.6% ST FL TRM 2: 51.6%

I've checked for vacuum leaks and found none. I used starter fluid on the intake runners and manifold areas, but there was no improvement in idle stability. My fuel pressure gauge reads 50 psi at idle, and when I depress the release button, it holds at 42 psi while running. I'm not sure where the snorkel is located — I sprayed cleaner on all connections to the air box, but that didn't affect idle performance. How should I check the EGR system? Thanks again, Joe

The key indicator here is your short and long-term fuel trims. Your fuel pressure appears to be too low — has the fuel pump ever been replaced? This could be contributing to the P0101 code and erratic idle behavior.

The 50 psi reading is from the fuel rail. What should the correct fuel pressure be? Also, based on the data list, is the MAF sensor functioning properly? The original fuel pump is factory-installed and doesn't hum or make unusual noise. Thanks again, Joe

Fuel pressure should be 55–62 psi with the key on and engine off, and 45–59 psi at idle. I've seen several technical service bulletins (TSBs) for the 2003 Chevrolet Express 3500 that describe similar symptoms — many point to a faulty MAF sensor. However, low fuel pressure can also cause these codes and abnormal fuel trims. Try running the vehicle with the MAF sensor disconnected and observe how the fuel trims respond!

Jeff, I unplugged the mass air sensor after warming up the engine, and the idle became smooth. The long-term fuel trim dropped to 15.6% for SLT TRM Bank 1 at 2. The short-term fuel trims fluctuated between -0.08 and +3.6%. What do you think? Thanks again, Joe

I'd recommend trying a new MAF sensor.

Jeff, I installed a re-manufactured MAF sensor from NAPA today, and the rough idle issue is now resolved. However, after clearing all codes and running the vehicle for several hours, new codes P0141 and P0147 have returned. What else could be causing this? Thanks again, Joe

A blown fuse in the O2 sensor heater circuit might be the issue, especially since these codes are related to oxygen sensor heating and lean conditions.