P0171 and P0300 Fault Codes on 1996 Chevrolet Z28 LT1 Engine: Diagnosis and Fixes for Older Vehicles
I own a 1996 Chevrolet Z28 with approximately 47,000 miles. I've been experiencing intermittent Check Engine light activation over the past few months. The light typically comes on during 2 to 3 starts before disappearing for 2 to 3 weeks, then reappearing again. Each time I plan a visit to the mechanic, the issue resolves itself. Using a basic OBD-II scanner, I've retrieved fault codes P0171 (System Too Lean) and P0300 (Random/Multiple Cylinder Misfire). Symptoms include a semi-rough idle, higher-than-normal engine temperatures in traffic, and an unreliable gas gauge when the fuel level is below one-quarter. While the latter two may not be directly related to the engine issues, they are noticeable. Prior repairs on this vehicle have included water pump replacement, radiator hoses, coolant level sensor, battery, and alternator—all of which were completed before this problem emerged. Based on forum search results, I've planned a basic maintenance routine: cleaning the Mass Air Flow (MAF) sensor, adding injector cleaner to the fuel tank, and performing a visual inspection of vacuum hoses. However, I'm curious whether older vehicles—especially those with low mileage—are more prone to specific wear issues such as dried-out gaskets or cracked rubber hoses. Are components like the catalytic converter or oxygen sensors particularly sensitive to age rather than actual driving conditions? Thanks for any insights or recommendations.
I suspect fuel pressure is below specification, and an inaccurate fuel sending unit could be contributing. Before attempting major repairs, I recommend checking fuel pressure and flow to rule out this possibility.