Possible Issues Related to the Tune-Up:
* Incorrect Ignition Timing: If the ignition timing was incorrectly set during the tune-up, it can lead to hard starting, sputtering, and rough running. The engine might be trying to ignite the fuel-air mixture too early or too late.
* Spark Plug Issues: Even new spark plugs can be faulty or incorrectly gapped. An incorrect gap prevents proper combustion, causing misfires and rough running. If the wrong type of spark plug was installed, that's another problem.
* Distributor Cap and Rotor Problems (if applicable): On older G20s with distributors, a cracked or worn distributor cap or rotor can cause misfires and starting problems. These were likely checked during the tune-up, but might have been overlooked or damaged during the process.
* Worn or Damaged Ignition Wires: Cracked or poorly connected ignition wires can also lead to misfires. These may have been disturbed during the tune-up.
* Improper PCV Valve Installation: A poorly seated or incorrect PCV (Positive Crankcase Ventilation) valve can affect the air/fuel mixture and cause rough running.
Possible Unrelated Issues (but potentially exacerbated by tune-up):
* Fuel Delivery Problems: A clogged fuel filter, fuel pump issues, or problems with the fuel injectors can all contribute to hard starting and rough running. The tune-up might have revealed a pre-existing problem that was masked before.
* Vacuum Leaks: A vacuum leak in the intake manifold or vacuum lines can significantly impact engine performance and starting. Disconnecting and reconnecting components during the tune-up might have created or worsened an existing leak.
* Faulty Sensors: Various sensors (oxygen sensor, mass airflow sensor, etc.) affect the engine's fuel-air mixture. A faulty sensor can lead to poor running. While not directly part of a tune-up, a poorly seated sensor connection or a sensor damaged during the tune-up can cause issues.
* Carburetor Problems (if applicable): Older G20s might have carburetors. Issues like a clogged carburetor, incorrect float level, or a faulty choke could cause these problems.
* Clogged Catalytic Converter: While less likely to cause hard starting, a severely clogged catalytic converter can restrict exhaust flow, leading to rough running and reduced power.
Troubleshooting Steps:
1. Double-check the tune-up: Verify that all aspects of the tune-up (ignition timing, spark plugs, wires, etc.) were done correctly and that no components were damaged.
2. Inspect for vacuum leaks: Carefully check all vacuum hoses and connections for cracks or loose fittings.
3. Check the fuel system: Examine the fuel filter, fuel pressure, and fuel injectors.
4. Inspect the ignition system: Test the spark plugs, wires, distributor cap and rotor (if applicable) for wear or damage.
5. Scan for diagnostic trouble codes (DTCs): Use an OBD-II scanner to check for any stored trouble codes. This can pinpoint potential issues.
If you're not comfortable performing these checks yourself, take the van to a qualified mechanic for diagnosis and repair. Provide them with details about the tune-up and the symptoms you're experiencing. This will help them isolate the problem more efficiently.
