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Throughout the years I've seen many threads without documented solutions on how to fix a poor idle. I have had surging idle issues as well as the dreaded idle dip/stall. I understand the frustrations of having such an issue but no definitive answers or guide to follow. When you attempt to fix your idle, do not half step. Do not skip any steps. I am confident that if you do all of these things you will fix your idle. You may not have the perfect idle but you will be very close to it. If any of you guys have any other solutions or experiences you would like to add in regards to fixing you idle issues please chime in.

Mechanical:

1. IACV: Clean your IACV thoroughly. Let it soak get out as much gunk as you can. Ensure it spins freely and add lubricant.

2. BLEED COOLANT: Make sure that there is no significant air bubbles in your coolant. Bleed the system thorougly. You can reference the service manual to learn how to do this correctly. The simple way is the jack up the front of the car as high as possible. Turn your temperature dial to hot so that coolant will flow through the heater core. Do not turn the fan on, (your simply turning the temperature dial from cold to hot, from blue to red).Take the cap off of the radiator. Start the car with all accessories off. Squeeze the upper radiator hose while the car is idle. I sometimes squeeze all the hoses that coolant flow through lol. You will see the air bubbles coming out the top of the radiator. I usually let the fans come on about 2 or more times before the system is fully bled.

3. CHECK FOR VACUUM LEAKS: Start the car, spray (highly flammable...be careful) carb/choke cleaner around the different areas of the engine bay such as hoses, throttle body, intake manifold etc. If the idle surges when you spray in a particular area you will have found your leak. rinse and repeat then repair. Pretty simple. Also be sure you are using the correct gaskets for you make/model/year, preferably new ones.

***Other mechanical and less common issues u can look for/do are to clean the throttle body thoroughly (avoid removing gray graphite coating used for creating a seal), check for a bad pcv valve, brake check valve, bad engine mounts, bad battery, alternator, eld etc.***

Tuning:

1. SET TPS: Make sure your TPS is set correctly. If you have a stock computer please follow the service manual procedure for setting the TPS. If you have KPRO, scale the tps in kmanager and ensure that it is between -1 and 0 when the pedal is not being pressed. I like to get mine as close to 0 as possible but never more than 0. It can be time consuming and frustrating to get this done but take your time. You may notice that you cannot get your TPS to be between exactly 0 and 100. That is fine as long as you have the min value set between -1 and 0. You maximum value may be more than 100. This would also depend on whether or not you have a stock TPS.

2. 0 DEGREE CAM ANGLE: Make sure you cam angles are at 0 degrees at idle. Do a datalog, look at columns where you car is idling and make sure that the camshafts are at 0 degrees. If they are not at 0. set that idle area to 0 degrees.

3. TUNE A/F: This is probably one of the most important aspects of a good idle. TUNE your A/F ratio. This will take time. It will take patience but if your air fuel ratio at idle is out of wack your idle will be poor. Make sure the fuel maps are as smooth as possible as well. Peaks and valleys will cause idle issues and overall less efficiency. Simply start the car, begin to datalog and observe your Long term and Short term fuel trims. Observe the A/F. Make the necessary changes accordingly whether it is adding or subtracting fuel. Get the short term and long term fuel trims to 0 at idle. *It is also a good idea to tune your partial throttle/ low fuel map as well for each cam angle to have an overall effecient map.*

4. IDLE VALVE DUTY ADJUSTMENT: In KPRO on the parameters tab under IDLE, Alter the idle valve duty cycle adjust slider value. Rev the engine to about 3000 rpm and release the throttle quickly. If the rpm drops below the idle speed and then recovers, then move the slider to the right. If the rpm drops to 500 above idle speed and then goes slowly down to idle speed, move the slider to the left. This slider will help you to fine tune your idle. Now every time you adjust this slider the ecu has to relearn your cars idle so give it a day or two and see how the idle settles out.

5. IDLE LEARN PROCEDURE: reference your service manual or simply browse the forums on how to complete this procedure. You can start the car and hold the rpms at 3000. Ensure all the accessories are off. When the fan comes on once the twice the car should have learned the idle. I do it the simple way and simply drive the car for a day or two. The car learns the idle quicker when the engine is warm.

6. IDLE SPEED: Hondata recommends setting your idle speed between 850-950rpm. Based on your engine mounts and the vibrations they give off etc you will have to use your discretion here.

7. IGNITION TUNING:
Hondata recommeds reducing ignition in your idle columns. I would suggest you use your discretion here as well and mess with ignition last if the other steps do no resolve your issue.

*HONDATA NOTE*
Note that after uploading a calibration the ECU takes a little while to learn the correct duty cycle for the idle valve (even if the upload is a very small change it resets the ECU's memory). If the car is hot then this learning process happens in a couple of minutes, but if the car is cold the ECU won't learn until the car is hot - and in the meantime, the engine sometimes stalls with large injectors. The trick is to not increase the idle speed too much to prevent the engine stalling if the engine is cold, because it will fix itself once the ECU learns the idle.

If you get a slight misfire at idle once the car is warm, slowly enrichen the idle target A/F ratio.
 

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Arouse the DAMPFHAMMER!
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Do not skip any steps. I am confident that if you do all of these things you will fix your idle. You may not have the perfect idle but you will be very close to it...
Cool stuff here, I appreciate your write up about the idle issue fixing here, Mr_Plenty :up:. This is a pretty complete summarize of what is to do with fixing a oscillating or stalling idle speed. I would just add a few things to it.

#1 sometimes the closed loop control of idle speed (fast track = ignition timing, slow track = IACV) get's distorted by aftermarket stuff (cams, injector size, ...) and the controller parameters should be adjusted but can't in KPro/FPro/Doctronic/..., then the rate of ignition timing change and increasing the allowed width of ignition timing could help to get it faster under control and calmed.

#2 check leaks at the exhaust manifold, interfering the lambda probe measurement and turn the engine into the too rich combustion at idle and further load points.

#3 check spark plugs/ignition system: color, gap size and condition. A gap size around 0.7 mm is a good value, the lower the weaker the spark. Beside a spark timing control of cylinder 1 (near auxiliary drive) by stroboscope testing, especially after reassembling cam, engine speed sensor and others and crank stuff also the ignition coil function can be an issue (dwell duration, hardware, ...) and need to be checked.

There are other points to add, but not for the check list which has an more general character. Just always think like the engine works. It need oxygen, fuel, spark and the control of these. Any of these systems can cause issues, just go through them - maybe on a paper to picture it - and ask what do they need and what not.
 

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Discussion Starter #3
Thanks for your additions @LotusElise.
I know the frustrations of a poor idle. It ruins the driving experience in every way. Many threads I have seen go unsolved. The fact that many people also began to suggest that a poor idle with dips and surges was “normal” or “ok” with swapped cars was upsetting. this is absolutely not the case. I created this thread so that it would be a great help to others. And hopefully over time more people add knowledge to this thread to bring forth more solutions.
 
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