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30,124 technicians on file · 885 cities · 51 states
The word is a leftover. A tune-up once meant points, a distributor cap and rotor, a carburetor set by ear and the timing dialed in with a light. None of that exists on a car built this century. The computer handles timing and fuel mixture, and it adjusts them thousands of times on the drive to work.
So what people call a tune-up now is a different job: replacing the ignition and intake parts that genuinely wear, and finding out why the engine runs badly. Spark plugs, ignition coils, the air filter, the fuel filter where the car still has a serviceable one, the crankcase valve, and sometimes a throttle body or injectors that need cleaning.
What brings you in is a symptom. A shake at idle, a stumble when you pull away, hesitation on the highway, hard starting on a cold morning, or fuel economy quietly sliding. Those symptoms have several possible causes, and only one of them is worn plugs. A vacuum leak, one failing coil, a dirty mass airflow sensor and a tired fuel pump all feel similar from the driver's seat.
The state and city lists below will get you to the shops near you. This is work people book when the cold weather arrives and the car starts complaining.
Spark plugs, and after that it depends on what the engine needs. Coils on a high-mileage car, the air filter, the fuel filter if yours can still be changed, the crankcase valve, and a clean throttle body if it is gummed up. There is no timing to set and no carburetor to adjust. Anything beyond parts replacement should follow a diagnosis, not a menu.
Usually one cylinder is not pulling its weight. A worn plug, a failing coil, a leaking injector or a vacuum hose that has gone hard and split will all do it, and so will a torn engine mount that lets you feel a perfectly normal idle. The shop finds it by seeing which cylinder is missing, then proving why. A parts swap without that step is a guess.
They do, just slowly. Modern iridium and platinum plugs last far longer than the old copper ones, so people forget them entirely, and a plug at the end of its life makes the coil work harder and kills coils. The interval is in your owner's manual. If a shop pulls one and it is worn, ask to see it next to a new one.
Start with the cheap answers: tire pressure, a clogged air filter, a roof rack you left on, and short trips in cold weather, which hurt mileage more than most people believe. After that it gets mechanical. A lazy oxygen sensor, a misfire you cannot feel yet, dragging brakes or a thermostat stuck open all cost you gas quietly. Fault codes usually point at the last group.
Much worse. A steady light means the computer logged a fault and you should get it read soon. A flashing light usually means an active misfire dumping raw fuel into the exhaust, which can destroy an expensive catalytic converter in a short drive. Pull over when it is safe, and get the car towed rather than driven if the engine is shaking.
Only if the plugs are the reason, and on a no-start they usually are not. Cranking but not firing points at fuel, spark or a crank sensor. Cranking slowly points at the battery or the starter. Nothing at all points at the battery, a connection or the ignition switch. Have it diagnosed before you buy parts; a hard start in the cold is a symptom, not a diagnosis.
