Fuel System Related (despite cleaning):
* Fuel Pump: A weak fuel pump can't maintain consistent fuel pressure, leading to surging. The pressure might be adequate at idle but falter under load.
* Fuel Filter: Even a new fuel filter could be clogged if the fuel system had significant contamination before the cleaning.
* Fuel Pressure Regulator: A faulty regulator can cause erratic fuel pressure.
* Dirty Injectors (Despite Cleaning): Sometimes injectors require more than a simple cleaning. They might have internal mechanical issues, or some injectors might be worse than others and still cause inconsistent fuel delivery.
* Fuel Injector Wiring/Connectors: Corrosion or damage to the wiring or connectors can lead to inconsistent signal to the injectors.
Ignition System:
* Ignition Coils: A failing ignition coil can cause misfires, leading to surging. This is more likely to cause a rough idle and hesitation than just surging, but it's possible.
* Spark Plugs (even after tune-up): Could be improperly gapped or damaged. Were they replaced during the tune-up? Incorrect heat range can also affect performance.
* Crankshaft Position Sensor (CKP): A faulty CKP sensor provides inaccurate engine speed information to the computer, leading to improper fuel delivery and timing.
* Mass Airflow Sensor (MAF): A dirty or faulty MAF sensor will send incorrect air flow readings to the engine computer, resulting in poor fuel mixture calculation which manifests as surging.
Other Possibilities:
* Throttle Position Sensor (TPS): A faulty TPS provides inaccurate throttle position information, leading to erratic fuel delivery.
* Throttle Body: Could be dirty or sticking. Even after cleaning, it could have internal problems.
* Vacuum Leaks: Leaks in the vacuum system can disrupt the engine's air/fuel mixture.
* Transmission Issues (Less Likely): While less probable given the description, a slipping transmission or torque converter can sometimes mimic surging engine behavior.
Troubleshooting Steps:
1. Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to read any trouble codes stored in the engine computer. This will give you a starting point.
2. Fuel Pressure Test: Have a mechanic test fuel pressure at idle and under load.
3. Visual Inspection: Carefully examine all vacuum lines, wiring harnesses, and components for any visible damage or leaks.
4. Data Logging: More advanced diagnostic tools can log various engine parameters (fuel pressure, air/fuel ratio, etc.) in real-time to pinpoint the problem.
It's strongly recommended you take your Silverado to a qualified mechanic. They have the tools and expertise to diagnose the problem accurately and efficiently. Trying to troubleshoot this yourself without the proper equipment could lead to further damage or wasted time and money. Mentioning all the work you've already done will help the mechanic focus their diagnostic efforts.
