It’s a tale as old as time — well, the automobile, at least — itself. You’ll be heading out on the open road, whether for your average commute or a lengthy road trip, and suddenly your car is making odd noises that it’s never made before.

Unfortunately, not everyone has the ability to strategically diagnose a vehicle’s maladies right there on the spot, and even with the advent of modern maintenance minders, many tend to ignore service intervals for too long. Changing the oil on a regular basis will only do so much, and because cars have so many moving components, keeping up with basic tune up needs can make a major difference in how a vehicle performs.

But plenty of people wait until something goes awry before taking their ride in for servicing. There are also numerous drivers out there who ignore a vehicle’s maladies all together, insisting that these issues will somehow work themselves out over time and that a fresh tank of gas and an oil change is all that their ride requires.

Don’t be one of these people. Your chance of doing even more damage to your vehicle skyrockets when a simple tune up issue goes ignored for prolonged periods of time. Here are four warning signs to watch out for on the open road, so don’t hesitate to schedule a visit to your local mechanic if any of them suddenly appear one afternoon.

1. The old shudder and shake

If your engine starts running rough when idling, or hesitates when the accelerator is mashed before overcompensating with a surge of power, it’s probably tune-up time. Clogged fuel filters, fouled-out spark plugs, faulty spark plug wires or coil plugs, and plugged-up air filters can cause this malady, all of which are relatively easy fixes on most vehicles.

2. A big-ass drop in MPGs

If one winter morning you wake up to find that your fuel gauge is dropping faster than the mercury outside, it’s time to check out your engine’s air filter, plugs, wires/coils, oil life, O2 sensors, and fuel filter. More than likely you will notice a gradual drop in fuel gains over the course of a few months, so start by running a full system cleaner through first in order to help flush things out, because it might be that you just have some nasty deposits.

3. The dreaded CEL of doom

That check engine light (CEL) is there for a reason, and while modern cars have maintenance minders, on older vehicles that warm yellow glow emitting from your dash could either mean cataclysmic engine failure or that it’s time for a fresh set of spark plugs. Even if your vehicle continues to run properly, if that light comes on, take it in for a diagnostic scan or an inspection anyway, because you probably won’t like what happens if you ignore it for too long.

4. You just can’t get it up (to speed) anymore

Neck-snapping acceleration is a magnificent experience that few drivers ever get to enjoy, but even in something pedestrian, the inability to get up to speed like you once did is a degrading sensation. Clogged fuel injectors, old air filters, sludge-filled oil pans, or compromised distributor points (on older vehicles) can all affect a car’s performance, so it’s typically best to start with the cheapest and easiest component to replace and work your way up.