Tune-Ups for Modern Engines

Decades ago, a tune-up meant adjusting ignition timing, points and the carburetor. Computer-controlled engines handle those adjustments on their own. So a modern tune-up focuses on the wear items that still matter: spark plugs, ignition coils and boots, air filtration, and making sure the engine computer is not storing faults that hurt performance or fuel economy.

A typical modern tune-up includes:

• Spark plugs: replaced at the interval in your manual
• Ignition coils and boots: inspected for cracks, carbon tracking and weak output
• Engine air filter: most schedules land it between 15,000 and 30,000 miles, and we replace it once it restricts airflow
• PCV valve and hoses: checked on engines where they are serviceable
• Throttle body: inspected for carbon buildup that causes idle issues
• Code scan: OBD-II has been required on cars and light trucks sold in the US since the 1996 model year, so we read stored and pending codes plus live data. Codes are five characters, and a P0 code is generic while a P1 code is manufacturer specific

Some engines also have fuel filters, valve clearance checks or other items on the schedule. We look those up for your engine.

Plan one when the spark plugs come due, or sooner if the engine runs poorly. The plug interval is set by the maker's schedule and varies widely with the engine and the plug metal, so we read it off your VIN instead of guessing. Symptoms like a rough idle, hesitation, hard starting or a drop in fuel economy are reasons to check sooner.

Signs your engine may need attention:

• Rough or shaky idle
• Hesitation or stumble when accelerating
• Hard starting, especially when warm
• A noticeable drop in fuel economy
• A steady or flashing check engine light
• A misfire you can feel as a jerk or shudder

If the check engine light is on, a tune-up is not automatically the fix. We read the codes and test first. A steady light is not an emergency, but it will fail a Smog Check, so it is worth sorting out before your test date. See check engine light diagnostics for how that works.

Spark plugs wear gradually. As the gap widens and the electrodes erode, the coil has to work harder to fire them. That extra strain can crack coil boots and shorten coil life. Worn plugs can also cause misfires, which waste fuel and can overheat the catalytic converter. Replacing plugs on schedule protects the parts around them.

When we remove plugs, we read them. Their condition tells us about the engine:

• Oil fouling: possible worn rings, valve seals or PCV trouble
• Carbon buildup: rich running or lots of short trips
• White or blistered tips: overheating or a lean condition
• Even light wear: normal

We photograph the old plugs for your inspection. Coils are replaced when testing shows they are weak or cracked, not automatically.

Engines with more miles benefit from a closer look at vacuum hoses, the PCV system, throttle body carbon and engine mounts, since those age alongside the ignition parts. Oil consumption and compression are also worth checking if the plugs show oil fouling. We add those checks when mileage or symptoms call for them and list them separately on the estimate.

Our high-mileage vehicles page covers other items that tend to come due as engines age, and preventive maintenance explains how to plan them.

A tune-up changes as the engine ages. Early on, it is mostly a scan and an air filter check. At the spark plug interval, plugs and coil boots become the main job. On higher-mileage engines, vacuum hoses, the PCV system, throttle body carbon and engine mounts join the list. Your owner manual sets the exact points; this table shows the general pattern.

Some engines put the rear spark plugs under the intake manifold, which makes the job longer. We look that up and tell you before you approve, so the time and the estimate make sense.

A tune-up done in a hurry can create the misfire it was meant to prevent. The usual culprits are the wrong spark plug type, plugs tightened by feel in an aluminum cylinder head, a cracked coil boot reused, or a single coil swapped without finding out why it failed. Careful work on these small parts protects the engine and the catalytic converter.

Mistakes we avoid:

• Wrong plug type or heat range. We use the plug the engine specifies.
• Adjusting fine-wire plugs roughly. Iridium and platinum tips break easily. We check the gap without damaging the electrode.
• Guessing the torque. Plugs go in at a foot-pound figure specific to your engine. Too loose and the plug can overheat; too tight and the threads in an aluminum head can strip.
• Reusing cracked boots. A tiny crack lets spark jump to the engine instead of the plug.
• Swapping one coil and walking away. A worn plug or a leaking valve cover can kill a coil. We look for the cause.
• Bottled fuel cleaners instead of testing. A cleaner will not fix a vacuum leak or a failed coil.

Many tune-up items connect to other systems. A clogged air filter is part of filters and fluids, and a misfire left too long can damage the converter, which leads to exhaust service.

If the engine starts to shake, stumble or lose power and the check engine light flashes, ease off the accelerator, avoid towing and steep climbs, and get the car checked right away. A flashing light means unburned fuel is reaching the catalytic converter, which can overheat it. A steady light with a mild stumble still deserves a prompt visit.

What to do, step by step:

1. Reduce speed and avoid hard acceleration.
2. Skip long freeway climbs if you can. The grades along the 210 put extra load on a misfiring engine.
3. Turn off heavy electrical loads if the car feels weak.
4. Note when it happens: cold start, idle, cruising or under load.
5. Call (909) 608-7699 and describe what you feel.

Commuters often notice a misfire first in stop-and-go traffic, when the idle turns rough at a light. Our commuter vehicles page covers other items that wear faster with daily freeway miles.