* Ignition System Issues under Load: This is a prime suspect. While the engine might run okay at lower RPMs in city driving, the higher demands of highway acceleration might reveal weaknesses.
* Worn Spark Plug Wires: These can develop cracks or internal damage that only becomes apparent under high voltage and stress from rapid acceleration.
* Weak Spark Plugs: Even new plugs can be faulty. While a tune-up included new plugs, a faulty set could cause misfires only when the engine is working harder.
* Ignition Coil(s): A failing coil might not consistently provide sufficient spark at high RPM, leading to misfires under load. This is particularly common in vehicles with multiple coils (one per cylinder or per pair of cylinders). Check for cracks or other signs of damage.
* Ignition Control Module (ICM): This component controls the spark to the plugs. A failing ICM can cause intermittent misfires, often more noticeable under higher loads.
* Fuel Delivery Problems under Load: Even with a new fuel pump and filter, other issues can arise:
* Fuel Pressure Regulator: This regulates the fuel pressure to the injectors. A failing regulator might not maintain sufficient pressure at high RPM, leading to lean fuel conditions and misfires under acceleration.
* Clogged Fuel Injectors: Although less likely given the recent fuel filter change, injectors can become clogged or partially obstructed, hindering fuel delivery under high demand. A fuel injector cleaner might help, but a professional cleaning or replacement might be needed.
* Air Intake System:
* Mass Airflow Sensor (MAF) Sensor: A faulty MAF sensor provides inaccurate air/fuel readings to the computer, leading to a poor fuel mixture. This often results in misfires, especially under acceleration.
* Engine Sensors:
* Oxygen Sensor(s): A faulty O2 sensor can cause incorrect fuel mixtures, resulting in misfires.
* Catalytic Converter: A clogged catalytic converter can restrict exhaust flow and cause back pressure. This can cause misfires, especially under heavy load conditions. This is less likely to be the sole cause, but it could exacerbate other issues.
Troubleshooting Steps:
1. Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to retrieve any stored trouble codes. This is the first and most important step. The codes will point you towards the most likely culprit.
2. Visually Inspect Components: Check the spark plug wires, ignition coils, and other visible components for any signs of damage, cracks, or loose connections.
3. Test Fuel Pressure: Have a mechanic or auto parts store test the fuel pressure at idle and under load (this often requires a special tool).
4. Check the MAF Sensor: Many auto parts stores can test the MAF sensor.
5. Consult a Mechanic: If you're not comfortable performing these checks yourself, take your Tahoe to a qualified mechanic. They have the tools and expertise to diagnose the problem accurately and efficiently.
The fact that the problem only appears during highway acceleration suggests a component that's stressed more under high RPM and load. Focus your efforts on the ignition system and fuel delivery components mentioned above. Getting those DTCs is crucial.
