PLEASE READ THIS FIRST BEFORE POSTING ABOUT HONDA IDLE ISSUES!!
This forum is flooded with questions about Honda idle issues so I’ve put together this ‘revised’ idle speech. This one is more for a hunting or erratic idle, the original speech was for a ‘shaking’ or ‘rough’ idle. For that check out the other link about Honda idle issues or type ‘Idle Speech’ into the search function.
Step 1 check for air in the cooling system. This is the most common cause of an idle issue on Honda’s. Especially if you just serviced the cooling system and by service the cooling system I mean replaced a radiator, water pump, thermostat, radiator hose, anything where you open the cooling system to replace a part. You MUST follow the procedure outlined in the video. It’s not important that you have a bleeder valve as those are really only there to make filling the system easier. You can skip that part if you don’t have a bleeder screw but you MUST follow the rest of the procedure to the letter in order to ensure you’ve bled all the air out. If you fail to bleed all the air out the idle issues will continue. If you find that the problem goes away after you bleed the air out of the cooling system but it comes back a few days later then check for a leak in the cooling system using the second video on checking for an overheat condition.
Next check for vacuum leaks. Vacuum leaks are the #2 cause of Honda idle problems. In fact I would say that all Honda idle problems are mixture related and vacuum leaks can be a big upset to the mixture at idle. Vacuum leaks add too much air to the mixture causing the engine to run lean. The computer also fights them as it tries to maintain an idle using the IAC but it can’t keep up so you get a ‘hunting’ idle condition meaning that the idle fluctuates from high to low and it never levels out. This condition is often worse after the engine warms up. When cold you just get an idle that is too high like up around the 1200-1500rpm range or higher. The second video shows a vacuum leak that I found on a Civic using a ‘safer’ method for checking for vacuum leaks. Both work but the important thing is that you check for vacuum leaks if you have a Honda idle problem. My bet is that you’ll have the problem solved in these first 2 steps.
If you’re sure you don’t have any vacuum leaks and you’ve bled the air out of the cooling system and you still have a problem then check the IAC (Idle Air Control valve). You can do this by tapping on it with the butt of a screwdriver while the engine is running. If the idle changes or stumbles in some way you may need to replace it. Many people try to clean them with mixed results. In short cleaning may not be the answer, you may need to replace it. Personally if I find a problem with one I just replace it. Cleaning CAN work if the pintle is getting bound up in some way but if the valve is having an electrical issue then you’re going to have to replace it no matter what. I should also mention that it could also be a connection or wiring issue so don’t forget to check those as well if you find the IAC to be the cause of the idle problem. BTW the Honda J series V6 engines from about 99-2004 are famous for IAC problems in fact you might even see a check engine light for it. If you do it’s a good idea to check it as I’ve outlined here and replace it if you find that it’s bad.
After that I check the operation of the PCV valve by pinching off the supply line to it with a pair of pliers. BTW Honda’s don’t like aftermarket PCV valves, in fact most times you’re better off with a used OE than a new aftermarket part. I’ve actually seen aftermarket PCV valves cause idle problems in some cases, usually a rough idle. The PCV valve is actually a controlled vacuum leak so if it’s not calibrated correctly it can cause idle issues. So if you’re running an aftermarket PCV you might want to exchange it for an OE unit. In my opinion the PCV valves on a Hondas are NOT a maintenance item, they either work or they don’t from what I’ve seen so only replace them if you find a problem. I do find problems with Honda PCV valves from time to time. The internals of the valve break apart sometimes and when this happens it causes a vacuum leak, a BIG vacuum leak at that, one that you won’t find by spraying around looking for a vacuum leak using the methods above. Hence the reason pinching off the supply hose fixes the idle issue, you’re really sealing off a vacuum leak when you do this if the PCV valve has come apart internally. If this is what you find replace the PCV valve with an OE unit.
I’ll just say straight out it’s not likely your idle issue has anything to do with the TPS (Throttle Position Sensor). The only time I’ve seen Honda TPS’s go bad is when they were physically damaged, someone tried to adjust it, or if it was an aftermarket unit. So if any of those conditions are true then by all means check the operation of the TPS, if not, leave it alone. One thing I do see from time to time that’s throttle related is someone adjusting the throttle cable too tight, either because they removed the throttle body to clean it or something similar. A quick check for this is to simply try holding the throttle closed at the linkage on the throttle body. If the idle calms down when you do this then it’s likely the throttle is not closing fully which can cause an idle issue for 2 reasons. The first is that it’s unmetered air that the computer has a tough time compensating for, especially at idle. The second reason is that this may upset the TPS reading which is important as it sends a signal to the computer telling it to go into idle mode. If the computer isn’t told to goto idle because it doesn’t see a closed throttle then idle problems will result as the computer doesn’t know it’s suppose to be controlling the engine functions for an ‘idle’ condition. Hence you get an idle fluctuation or it may not idle at all. Here’s a video that will help with the throttle cable adjustment procedure.
EGR will not effect idle unless it’s stuck open. Many people go here but to be honest it’s hardly ever the cause of an idle problem on a Honda. When the EGR is a problem it often causes a miss under load NOT an idle issue. I’m not saying you don’t need to check your EGR ports from time to time as they do clog up but EGR is NOT active at idle so it should not have any effect on the idle unless it’s stuck open as I’ve stated. Even though this post is about Honda idle issues I’ll post the videos I have about cleaning EGR passages on both the 4 cylinder and V6 Honda engines just for good measure.
The FITV (Fast Idle Termo Valve) is one of the LAST things to check. The most important part of the procedure is to back it off 1/4 turn after you bottom it out. You won’t find one of these on EVERY Honda engine BTW, mostly on engines older than 1997. The later model engines just use the IAC to control fast idle on a cold start up. This one can often save your butt but if you go too tight you won’t have a good idle when the engine is cold. The adjustment procedure is in this video.
It’s also a good idea to watch this video before adjusting the FITV.
Lastly don’t adjust the idle screw! This often gets done first thing and can actually mask the fix when you finally do fix the idle problem. If it looks like someone has messed with the idle adjustment screw perform the idle relearn procedure. Depending on the model you normally unplug the IAC after the engine is fully warmed up and adjust the idle screw until you reach base idle which is normally in the 700-750rpm range. This will often set a CEL so you’ll need to reset that after you’re done. Also don’t plug the IAC back in till you shut the engine down to help protect the PCM. Consult the service manual for the vehicle you’re working on for specifics on resetting base idle.
Notice I haven’t said anything about the MAP (Manifold Absolute Pressure sensor). This is because once again this is not a common problem on Honda’s and once again it’s external damage or aftermarket parts that I normally find fault with. An erratic idle CAN set a MAP sensor code however which is why I mention it. The reason for this is because the MAP is in essence a vacuum gauge so if it’s gets strange readings from a fluctuating idle it can set a MAP sensor code. This is not common but I feel it’s worth mentioning because I have a lot of people say the replaced or worse yet, CLEANED the MAP sensor to correct an idle problem. Don’t clean a MAP sensor, you’ll likely ruin it if you do. If you have a CEL with a MAP sensor code and a fluctuating idle, address the idle issue first, reset the code, and see if the MAP sensor code comes back. My bet is that it won’t come back after you get the idle problem solved.
Lastly don’t rule out a mechanical issue. If you get an idle issue after say you replace the timing belt and water pump first check for air in the cooling system, if you don’t find any check the mechanical timing. If you’re off a tooth with your belt it is possible that will cause an idle problem. In addition if the engine has bad valves or a compression problem this can also cause an idle issue. I would check all of the above suggestions first however but don’t rule out a mechanical problem if you do all the above checks and still have an idle problem. If the engine isn’t working properly then it can cause all kinds of other problems not to mention idle problems.
Thanks for reading and good luck. I hope this information helps with you solve your Honda’s idle issue. If you feel that you need more help with this feel free to start a thread in this forum, we’ll be happy to help.
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