Have you ever wondered what your RPM’s should be while your car is idling? Maybe you are experiencing some issues of engine stalling, or seeing unusually high RPM’s while sitting at a stop light? Whatever your interest or dilemma is, we’ll get into the discussion of idle RPM’s throughout the following article and provide some helpful insight.
What is RPM ?
To start with lets establish what RPM stands for, specifically in regards to the engine in your car. RPM stands for revolutions per minute. Revolutions of the crankshaft upon its axis, to be precise. Typically, your RPM’s can be viewed with the tachometer on the dashboard of your car, if so equipped.
Depending on the vehicle and/or engine in question, there is a redline RPM range shown on the tachometer somewhere between 5,500 and 7,000 RPM’s for an average passenger vehicle. If the engine is pushed into this limit, there is a high chance to critically damage internal engine components.
Potentially enough to be catastrophic on engine functionality. These days, it is common for vehicles to be equipped with a rev limiter which prevents the engine from performing above recommended RPM’s the engine was designed for. It still remains true that to prolong the life of an engine, keep it out of the redline. At least as far as the average daily driver is concerned.
Idle speed is the rotational speed of the running engine while at rest, meaning the engine is not coupled to the drivetrain of the vehicle and the throttle isn’t depressed. There are many factors that factor into what idle speeds should be expected. For the majority of passenger cars, idle RPM’s should be somewhere between 600 and 1,000 RPM’s. Motorcycles usually see a range between 1,200 and 1,500 RPM’s for a single cylinder engine, and around 1,000 RPM’s for a two cylinder. More heavy duty vehicles typically hover around 600 RPM’s.
These approximations can vary, however, if the vehicle in question is operating a significant number of accessories or sub-systems such as air conditioning. With additional accessories comes additional engine idle speeds. It isn’t uncommon to see a variation in idle RPM’s between engine startup and after the engine is warmed up. RPM’s are going to be slightly higher when starting an engine cold.
There is a reason for the simple explanations above. They exist to provide you with some notion of what to expect to see from your vehicle, whatever it is that you drive. There are times, however, when certain systems of our vehicles don’t follow what we consider to be normal or expected. It’s possible to see your tachometer read much lower or much higher than the guidelines listed above. Let’s find out what it could mean for both of these extremes.
If your car is seeing low RPM’s, chances are your car is also sputtering, misfiring, or possibly even stalling out completely. There are a few things that can cause this. There could be a vacuum leak contributing to the problem. If your vehicle is equipped with an EGR Valve (Exhaust Gas Recirculation), it may be clogged, dirty, or just be in need of replacement. A very common cause for low idle is a defective IAC Valve (Idle Air Control). Repair costs for these items can vary quite a bit, so it’s best to consult a professional for replacement part costs for the correct part for your vehicle.
The other side of the coin is a higher than normal idle speed. A few of the common causes here can be similar to the causes for a low idle, as discussed above. Vacuum leaks as well as a bad IAC Valve could just as easily cause high idle speeds. A faulty throttle system can also be a culprit. If none of the above seem to fit the bill, check out your air intake for any cracks or excessive amounts of dirt and debris. Lastly, one cause you might not expect to cause high idle speeds, is a defective alternator. Again, consult a professional if diagnosing these issues is above your skillset and comfort level.