Solving Automotive Idle Problems
I’m not a fan of dump-in-the-tank fuel injector cleaners and octane boosters. I’m not saying that they’re bad and not to use them. I suppose they work to some degree, but not as well as my professional setup does. Am I saying you need an expensive professional fuel injection cleaning system to get the job done? No, but it’s the best method I’ve found so far.
As for octane boosters, I really don’t see the point. The RM2 octane rating is a rating of resistance to burning. The higher the octane, the less the fuel wants to burn. You only need high-octane fuel with high compression or forced induction engines. Some people swear by octane boosters and running high octane fuel, if that’s you, more power to you (pun intended). For daily drivers, all you need is regular octane and your engine should run just fine, in some cases even better. Here’s a video with some details on that.
Now that you know how the PCV system works, we can talk about some of the problems it can cause with your idle should it fail. I have seen occasions in which a PCV valve came apart internally. In essence, what this caused was a vacuum leak, which can cause all kinds of idle problems.
An easy way to check for this is to pinch off the vacuum supply line to the PCV valve itself. If your engine idle smoothens out when you do this, replace the PCV valve and see if that solves your idle problem. When it comes to PCV valves, the shaking method is not accurate and tells you very little.
As far as Hondas go, if you replace the PCV valve, I strongly recommend using an OE (original equipment) replacement. I’ve actually seen issues with some aftermarket PCV valves on Hondas, so to avoid this, go with an OE part. Also, Honda PCV valves don’t often have problems, and for that reason I don’t recommend replacing them as part of a service. I only recommend replacement of a Honda PCV valve if there is an issue with the valve itself.
Some newer vehicles don’t have a replaceable PCV valve. These engines usually have a baffle system in the valve cover that functions as the PCV. I’ve only really seen this type on vehicles in the 2000 model year and up, and not on engines older than that. That doesn’t mean they don’t exist. The servicing of these systems is specific to the vehicle, so check your service manual on how to diagnose and service your particular system. I’m going to be honest and say that I don’t have a lot of experience with these systems, but I haven’t seen one cause an idle issue yet. I’ll update this article if I do.
EGR problems can sometimes cause idle issues. However, this will only happen if the EGR is stuck open. If it’s stuck closed, or not operating correctly, it should not effect the engine idle. If however the EGR is stuck in the open position it will add exhaust gases at idle, upset the idle mixture, and cause an idle problem. Usually a rough idle. A quick way to check for this with the old style diaphragm EGR is to pull up on the diaphragm of the valve as the engine is idling. If the idle changes or the engine stalls, the EGR is working properly and is not the cause of the problem. You can also apply vacuum with a vacuum pump to the EGR valve if you can’t pull up on the diaphragm in the valve. The results would be the same no matter what method you choose. If you have no change when you manually activate the EGR it could mean a couple of things. The first is that the EGR valve has failed mechanically and should be replaced. The other possibility is that the passages that feed the EGR gasses back into the intake are clogged and not allowing EGR gasses to flow into the intake. Either way, this is an EGR issue and should not effect your idle. If you have an electronic EGR valve, testing will be different. You may be able to activate it with a bidirectional scan tool to verify it’s operation. This testing will vary depending on make and model and also if you have a scan tool capable of commanding the EGR to operate. It would be best to consult the service manual for the vehicle you’re working on to verify EGR operation if you have the electronic type. As stated, the only way EGR effects the idle is if it’s stuck in the open, or partially open, position.
As stated earlier, issues with some of the sensors listed at the beginning of this article can cause an idle issue. So if you have a check engine light on for any one of those systems or sensors and you have an idle problem, fix what’s causing the check engine light to come on and recheck for the idle problem. Lots of people go for the TPS (throttle position sensor) if they have an idle problem. I say if you don’t have a code for it, look elsewhere first.
Before you replace a TPS, first check to make sure it’s functioning properly. There is a mechanical issue that can cause the TPS to not read correctly: an improperly adjusted throttle linkage. Though this will cause the TPS to not read correctly, the sensor itself is good. Normally, you would not adjust a throttle cable, but say you just removed the intake manifold and had to remove the throttle cable to perform that repair. If it’s not reinstalled correctly, it can cause the TPS readings to be off, and as a result cause an idle problem. The computer needs to see that the throttle is closed before it sets the engine idle. If it doesn’t see a closed throttle, it will never go into idle mode. Here’s a video on throttle cable adjustment that you might find helpful if you run into this problem.
Another common sensor issue that can cause idle problems is the coolant temperature sensor. There are a few acronyms for this, such as the CTS (coolant temperature sensor) or TW (temperature water) sensor. Different manufacturers call it different things, but its function is the same. Coolant temperature sensors monitor coolant temperature and send the readings to the computer. It’s probably one of the most important inputs to the PCM.
The coolant temp sensor is kind of like the choke on an older carbureted engine. As the engine warms up, different things begin to happen or need to happen. Engine temperature is the cue for many of the events in a fuel injection strategy. With fuel injected applications, engine temperature is critical to many engine functions. If you have an idle problem and a CEL (check engine light) code for the coolant temperature sensor, address the coolant temperature sensor and then recheck for the idle problem.
In addition to coolant temperature sensor issues, O2 sensors can also be the cause of an idle issue. When the engine goes into closed loop, the computer uses the O2 sensor as its main input for calculating a fuel mixture. If the O2 sensor is having an issue, it can cause an idle problem. So once again, if you have an O2 sensor code and an idle problem, solve the O2 sensor problem and recheck for the idle issue. Here’s a video on how O2 sensors work that you might find interesting.
Another sensor I’ll mention is the MAF sensor, or mass air flow sensor. This sensor actually measurers the amount of air going into the engine. This measurement is used to calculate the fuel mixture. If you know how much air is coming in, you can calculate a fuel mixture to go with it. If this sensor has an issue, it can cause idle problems.
In addition to problems with the sensor itself, you also need to look for air leaks after the sensor and before the throttle plate. Any leaks here will offset the measurement the sensor made of the incoming air. The term for this unaccounted-for air is “pirate air.” This extra air can offset the air fuel mixture and cause an idle problem.
If you don’t find any leaks and you suspect an MAF sensor problem, you can clean this sensor instead of replacing it. Depending on the sensor’s malfunction, this can sometimes work and actually make your engine run better. The MAF sensor uses sensitive electronics in the incoming air stream to take its measurements. If these components become dirty, the sensor cannot read efficiently. Cleaning the sensor can sometimes correct this problem. So if you suspect a MAF sensor problem or you have a check engine light with an MAF sensor code, address that first, then recheck for your idle problem.
I could go on sensor by sensor, but I think you get the point. If you have a check engine light on and an idle problem, solve the check engine light first and then recheck to see if you still have an idle issue.
Video Title: Solving Automotive Idle Problems – EricTheCarGuy Video Description: In this Article, Solving Automotive Idle Problems, Eric looks at what can be the cause of Solving Automotive Idle Problems with your vehicle .Thumbnail: http://www.ericthecarguy.com/images/faq_buttons/Large_FAQ_Images/Idle-Issues-icon-large.png