Solving Automotive Idle Problems
Fuel Injector Cleaners, Octane Boosters
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.
The PCV System
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
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.
Sensor Problems
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
19 thoughts on “Solving Automotive Idle Problems”
RJ
February 13, 2024 at 6:18 am
Hello Mr car guy i have a 92 honda civic that when it warms up it will idle like its about to die ive replaced the fuel filter the fuel pump i checked the iacv i replaced the spark plug wires about 2 years ago along with the spark plugs and it just recently started acting up where should i check next??? Please i would really appreciate your help
Wes Crews
October 27, 2023 at 11:34 pm
Hello,
Vehicle in question: 2002 Honda Odyssey. Problem: originally no start condition.
Remedy as per your video – repaired solder joint in main relay .Vehicle now runs but has a bouncing idle.
Checkers power steering pressure switch wiring.. all ok.
Would a defective IAC valve cause this issue ? If not ? What else?
I’m stone walled. BTW… no DTC codes present.
Would sincerely appreciate any advice or pointers.
Absolutely love the videos.. they have been a tremendous help.
Hope to hear back.
Wes in MS
Ron Kanna
May 22, 2023 at 3:14 pm
1995 Accord 2.2l VTEC
My idle surges from 1000 to 2500 constantly until I unplug my IAC valve. I have cleaned my egr ports and tried a new IAC valve but I still have the same problem? Something is telling the valve to stay wide open when it is plugged in??? Could a temperature sensor be causing it?
The only thing I can think is that I put a new aftermarket IACV on and it is also faulty?? I find it hard to buy a $300 part when that might not be the problem??!! I also replaced the IAT sensor, the temperature sensor and put a different throttle body on, I have bled the cooling system several times and it STILL SURGES!! Sometimes I can hold the rpm’s at about 4000 for several seconds and then it will idle down but only until I give it more throttle then it starts surging again???
James
March 25, 2022 at 3:36 pm
2002 accord V6 j-series sat for a year. New alternator, battery, fuel, pump, spark plugs, etc. idle surge issue and when it happens the TCS light comes on as well.. any ideas? IACV probably
John
January 26, 2022 at 11:56 pm
I’m having a problem with a 2002 Acura TL type-S. I have codes P0505 and P1519, saying there’s a problem with the IACV. The car is surging at idle, from 1k to 2k RPM. I cleaned the throttle body and the IACV valve and did not help. Replaced the IACV and did the idle relearn procedure and still doing the same. Replace the FICV that right below the IAC and improved a little. It now starts at high RPMS, then starts to surge for s few minutes, then stays between 1450-1550 RPMS. Only does it in Park and Neutral. I’ve checked electrical connections and everything seems fine. Have checked for vacuum leaks or EGR problems and didn’t find anything out of the ordinary. Have replaced and bled the cooling system in the process also. Any suggestions on what to check?
Gage
March 26, 2023 at 1:25 pm
I had have the same problem which left me very clueless on what to do after changing my MAP Sensor along with IAC Valve I proceeded the idle relearn procedure and still nothing untill when I just started to hit my throttle body and the idle have just went back down to regular idle which was at 845 for mines. That’s when I’ve notice my throttle body is going bad. I had changed my throttle body, done the relearn procedure drove for 10 miles and bam it was fixed. Before It would just throw P0505 code. Hope this helps
Kenneth DeLome
October 4, 2021 at 11:30 pm
ok so my daughter has a 06 scion s/a it has been running as it should and now she is having a issue under a load and at a momentary idle im somewhat savy with motors but mostly chevys with that said i go with my gut and want to start at the tank…. thoughts …. this problem just started about 2-3 days back when she was running late to work and ran low on fuel on her way after work.
Oscar Talamayan
September 10, 2021 at 5:13 pm
Own a 2010 Camry LE 2.5L 4cy. Issues are :
Car ENGINE TURNS OFF
1. while making sharp nor slight tuns
2. Engine turns off suddenly for a block straight driving.
3. When car Stalls it can turn engine on again.
4. Car Stalls only when driving
5. When parked, No lights in dashboard. Normal idling. Don’t Stalls and rpm at steady 6,000
Please Help
Zack lowe
July 20, 2021 at 7:31 pm
Having a problem with my 2000 Honda Civic ex when it’s in park and ac is on the car sounds like it wants to stall out and the idel tends to jump. when the ac is off the idle is fine it idles at 500-1000 rpm could it be my (IAC) ?
ron
February 12, 2021 at 3:22 pm
i am currently having this issue. 2003 honda crv 2.4 UK manufactory model. things ive tried, 1)purchased the $300 oem iac , 2) iac relearn procedure 2sec on then 3k rev for 10 without any load, 3) removed the ecu/pcm fuse for 5 min then replace and tried the relearn again, 4) check for vacuum leaks, 5)replaced the pcv incase this was the issue. i initially removed the old iac cleaned it and installed with no luck, this is why i bought a oem replacement. One thing i’ve noticed, when i erase the p0505 code with obd scanner, the crv idles perfect until driven and the check engine light comes back on. hopefully you may have some insight. thank you in advanced
Paul Petty
December 22, 2020 at 12:21 pm
I have a Nissan Altima that won’t will crank but won’t stay running,if I hold the throttle down it will run but I’d I release the throttle it dies…please helpppp
Leon Witherspoon
September 4, 2020 at 8:41 am
Hey hi everyone, I owned an 95 Honda Civic EJ1 D16y8 block with Z6 head. My problem is that when I started the car it idles fine but once at operating temperature it idles down and shut off. Any help would be appreciated.
Shaquille Smith
August 29, 2020 at 4:03 pm
My 2000 honda accord is just surging i change the water pump now i put everything back together start one crank but the idle just keep reviving ive clean the idle control valve an intake an throttle body with carb cleaner but it still surge up an down from 1500 to 2000 rpm can u help
Uzi
July 30, 2020 at 3:48 am
Hi ERIC hope you will be doing fine…. i am having a issue with my idle with AC on it drops badly while AC and stays low idle with AC on can you plz help me out…. plz plz plz
Donald
July 24, 2020 at 7:45 am
Hello! I have a 1993 Honda Civic EG6. I have an idle problem on it. the engine is sucking. Anyone have this experience and how to solve it.
Juneju gacutan
July 13, 2020 at 2:34 pm
Hi! I have a honda civic lxi 1998 model automatic. My oroblem is that when i turn-on the AC, it will shut down. Kindly advise. Thanks in advance
Sam
June 25, 2020 at 9:47 pm
Short and sweet 1993 Honda Accord CB seven. No modifications EX model. I am having the idle issue that is all so common where it fluctuates after it warms up a bit. I have a replaced the idler units in the front of the intake manifold and cleaned throttle body. check for water leaks and air leaks.With no avail. I have purged my water system. I have a video of me running the car and then putting my finger over the top hole in the throttlebody on the side closest to the firewall and idle drops and stays perfect. Does this mean I need to replace the throttle idle sensor?
Billy
June 7, 2020 at 3:48 pm
I have a 2005 Silverado 1500 5.3l V8, recently when I am driving and I come to a stop light and im just sitting there in Drive, my battery gauge will move back and fourth and will have a slight rough idle to it when only the gauge is moving, the battery is brand new, what could it be? I know I have stuff plugged in to my 12v ports that I use, the battery gauge doesn’t drop below 14
Dylan
March 13, 2020 at 4:47 am
Hi, I was changed my mini cooper s r56 oil filter housing gasket and oil feed line and return line. But I foud the turbo is not like before have power, especial I cannot hear the dump valve sound and wastegate looklike not working. the code is P112B, p0340 and p2188. when I was changed before only have p2188.