2001 Chevrolet Silverado 1500 Z71 After Tune-Up: Multiple Engine Codes P0101, P0102, P0161, P0171, P0174, P0300, P1258, P1404, and P1637

You replaced spark plugs and wires, and suddenly started seeing multiple codes. Were there any error codes or check engine light issues before the tune-up? Did you perform any other modifications or repairs recently? I'm asking for a clear starting point. Do you have access to a diagnostic scanner? Looking at live data from sensors like MAF, TPS, and EGR would be critical. Specifically: - DTC P0101: Mass Air Flow (MAF) Sensor Performance Issue - DTC P0102: MAF Sensor Circuit Low Frequency - DTC P0161: HO2S Heater Performance Bank 2 Sensor 2 - DTC P0171: Fuel Trim System Lean Bank 1 - DTC P0174: Fuel Trim System Lean Bank 2 - DTC P0300: Engine Misfire Detected - DTC P1258: Engine Coolant Over Temperature - Protection Mode Active - DTC P1404: EGR Closed Position Performance Issue - DTC P1637: Generator L-Terminal Circuit Fault

I performed the tune-up because one of the intake boots had a heat shield missing and a visible hole that caused arcing every time I started the truck. As a result, I replaced all spark plugs and wires and added a proper heat shield to the boot. I first replaced the throttle position sensor (TPS) as recommended by O'Reilly's—after which it ran smoothly for about 20 minutes before developing idle instability and a strong gasoline smell, along with excessive fuel consumption.

Why was a TPS replacement made if there is no P0102 code? Are you using an electronic throttle (fly-by-wire) or a traditional throttle cable? Did you use AC Delco spark plugs and wires? Is the engine overheating? You have a 195°F thermostat installed. Are you using any aftermarket air filters like K&N? Is the alternator connector properly connected—tight, clean, no corrosion? Again, do you have access to a diagnostic scanner for live data monitoring?

I replaced the TPS based on O'Reilly's initial diagnosis after the plug and wire replacement. I used Bosch spark plugs and MSD wires—no AC Delco parts. The thermostat is set to 195°F, and I have no K&N or similar air filters. I will check the alternator connector for tightness and corrosion. However, I currently do not own a diagnostic scanner and am unsure which model to purchase.

Let’s take a step back: Check all electrical connectors at the alternator, MAF sensor, and EGR valve. If there's no overheating issue, drive the truck to a parts store and get correct OEM-style plugs and wires. Get a can of throttle body cleaner and brake/carburetor cleaner—use them to clean the throttle body and intake components. Have the codes cleared at the shop. Then monitor whether they return. Pay close attention: Is the check engine light on? After clearing, does it go out? Ideally, we want the CEL to turn off for a fresh test—avoid hard stops or sudden acceleration that might prevent the light from resetting. A diagnostic scanner is essential today. Consider models like the Actron CP9580 or similar. Would you be open to discussing one with your local auto parts store? Also, do you have access to a fuel pressure gauge? This would help assess fuel delivery and support further diagnostics.

Thanks, kev2—I’ll check those items after lunch and get back with updates.