Ignition System Possibilities (but less likely given the symptoms):
* Weak Coil: A weak coil might provide enough spark at idle, but not enough when the engine is under load (accelerating). This is a possibility but less likely than fuel issues.
* Worn Distributor Cap and Rotor: These components distribute the spark to the spark plugs. Worn components can cause misfires under load.
* Ignition Module (Electronic Ignition): Similar to a weak coil, a failing module may struggle to provide sufficient spark under higher demands.
* Worn Spark Plugs and/or Wires: These are fundamental to ignition. Worn plugs or wires can lead to misfires, especially under increased load.
More Likely Culprits (Fuel and Air):
* Fuel Pump: The fuel pump might be weak and unable to supply enough fuel when the engine demands more during acceleration.
* Clogged Fuel Filter: A restricted fuel filter will starve the engine of fuel under load.
* Carburetor Issues (if applicable): If it's a carbureted engine, several things could be wrong:
* Clogged jets: Restrict fuel flow.
* Vacuum leaks: Lean out the mixture.
* Accelerator pump malfunction: Doesn't provide the extra fuel needed for acceleration.
* Throttle Body Issues (if fuel injected): Similar to carburetor problems, a dirty or malfunctioning throttle body can restrict airflow or fuel delivery.
* EGR Valve (Exhaust Gas Recirculation): A stuck-open EGR valve can cause a lean condition, especially at higher engine loads.
* Mass Airflow Sensor (MAF) or MAP Sensor (Manifold Absolute Pressure) Issues (if fuel injected): These sensors measure air intake and if faulty, can cause improper fuel/air mixture.
Troubleshooting Steps:
1. Check the basics: Start by inspecting the spark plugs and wires. Are they worn, fouled, or damaged? Replace if necessary.
2. Listen carefully: Does the engine sputter and die, or just cut out abruptly? A sputtering sound suggests a fuel problem; an abrupt cut-out might point towards ignition.
3. Check fuel pressure: If you have the tools, measure fuel pressure at idle and then during acceleration. A significant drop in pressure during acceleration points to a fuel delivery problem (pump or filter).
4. Inspect the air filter: A severely clogged air filter can restrict airflow and cause similar symptoms.
5. Check for vacuum leaks: Listen for hissing sounds around the intake manifold and carburetor/throttle body.
6. Start with the most likely and easiest checks: Fuel filter is cheap and easy to replace. Spark plugs and wires are relatively simple too.
Without more information (car details, type of fuel system), it's impossible to give a definitive diagnosis. Start with the simple, inexpensive checks and work your way through the more complex issues. If you're not comfortable working on your car, take it to a mechanic. Describing the problem accurately to them will help them diagnose the issue quickly.
