Your car has been running great for years, but recently it has developed a rough idle. The tachometer needle jumps erratically, and the engine surges and wanes. There are some definite causes for the rough idling, and the problems may be simple to repair. Not correcting this problem now may lead to serious engine damage later, leaving you stranded by the side of the road.
A loose or broken vacuum hose causes rough idling, and is the easiest repair of all. This is a very common problem since hoses wear out over time. Look in your engine compartment, and examine the hoses carefully for any signs of abrasion, breaking or loosening. Replace any damaged or broken sections of hose, available at most auto parts stores, and your rough idling will more than likely disappear.
Clogged filters are another common cause of rough idling. Inspect your air filter. If dirty, replace it. Also, a clogged fuel filter causes rough idling. It's hard to tell if a fuel filter is clogged or not, so a good rule of thumb is to change it at every general tune-up.
Bad spark plugs, bad spark plug wires and a bad distributor cap are other common causes of rough idling. If it has been a while since you changed these components, do so. Most auto service centres can do this for you if you need technical expertise.
A timing belt jumping a tooth is also a cause of rough idling. This throws off cam timing, setting in motion a series of events that prevent your engine from achieving proper timing. This is a more in-depth repair and, if needed, should be referred to a qualified auto mechanic.