Still having idle issues, help please

[Jinks]

Hey folks,

I am still having a bit of an idle issue with my freshly built beast. I’m not sure if it is an idle issue though or not. The car when sitting, idles just fine with or without ac and under load the motor is just ridiculously strong. But for some reason when I slowly build rpm up to about 2k/3k and lift off throttle, the motor drops to 200 rpm and almost stalls but not always. Like in stop and go traffic. I have the idle screw adjusted at the highest point to counteract this so the motor doesn’t stall. Shad and I spoke about maybe an idle air control valve being the issue. Can anyone chime in here to point me in the right direction? I’m not sure if it is a tuning issue or a mechanical issue? I hope it isn’t a tuning issue because the car is just brutal in acceleration and I do not wanna change it. Vacuum leaks and dirty throttle body would probably not be the case as the whole entire motor was broken down and cleaned with fresh parts. The car is on sos ems 2 engine management.


Any Help is greatly appreciated. Thanks.

 

[RYU]

In almost all cases of standalone ECUs that i'm aware of, idle, partial throttle issues don't have any bearing on the WOT tuning so you ought to be safe there.

The IAC valve is actually pretty easy to service if you want to get in there. I cleaned mine off with generous throttle body cleaner (some say this isn't safe, some say it is YMMV).

Wish I could help more...

 

[Jinks]

In almost all cases of standalone ECUs that i'm aware of, idle, partial throttle issues don't have any bearing on the WOT tuning so you ought to be safe there.

The IAC valve is actually pretty easy to service if you want to get in there. I cleaned mine off with generous throttle body cleaner (some say this isn't safe, some say it is YMMV).

Wish I could help more...

Yes. I’m not worried about the tune or WOT because it is tuned on the rich side. It’s more a nuisance to me. I do not like the car nearing a stall. I’m wondering if I should change the IAC valve? It pisses me off in traffic.:biggrin:

 

[Old Guy]

I agree with RYU, the first thing to do would be to check to make sure that your Electronic Air Control Valve is actually operating. Check to see that you are getting voltage at the EACV connector and check to make sure that the coil in the EACV has not gone open circuit on you. Try cleaning the air path if it looks dirty - maybe the actuator is sticking making it slow to respond when the engine speed drops.

Normally I would say check the factory service manual for the idle set up procedure; but, you don't have the OEM ECU so that probably does not apply. EACV operation is controlled by the ECU. Do you know how idle control is set up in the ECU or is this one of those 'tuner locked' arrangements where the tuner hides their configuration secrets from everybody? If the latter I think you are on your own, or dig up the phone number for your tuner to find out what they did.

You said the engine drops to 200 RPM and almost stalls. Does that mean that if it does not stall that the engine speed recovers to the normal idle speed? If so, the tuner may have implemented fuel cut on lifted throttle and the ECU is not restoring fuel fast enough when the engine speed drops down.

If you need to genuflect at the feet of your tuner because all of this stuff is secret, you might ask them whether they implemented fuel cut and what the restoration points are and if the restoration points are really low then can you move them up. If you don't have fuel cut enabled then fuel cut is clearly not the cause of your problem. In that case, I would be focusing on the control and operation of the EACV.

 

[mwagner10702]

Here is an interesting post from @Honcho.

http://www.nsxprime.com/forum/showthread.php/178307-Intake-Manifold-Overhaul

May be a helpful reference.

 

[Jinks]

@Old Guy, thanks for jumping in. I do not believe there is a fuel cut function. According to Shad my tuner, the car didn’t have this issue, so I am leaning on the side of mechanical issue. But the car was tuned in Rancho Cordova,California then shipped to South East, Florida. When the engine nears stall, it immediately corrects itself. It’s very strange. It only does this when slowly giving throttle, then quickly lifting throttle. When in gear, it does not do this. Only when I pull it out of gear and coast or when in neutral and parked. When in gear, the car just pulls like an ox and there is no problem. As mentioned, the car is tuned on a rich side. About 12.7 afr in WOT.

Also, I wanted to add that when revving the car it does not do this. Only when slowly giving throttle then lifting off.

 

[Jinks]

Here is an interesting post from @Honcho.

http://www.nsxprime.com/forum/showthread.php/178307-Intake-Manifold-Overhaul

May be a helpful reference.

Thanks. I looked into this thread while doing a search. Oh the joys of aftermarket.
But there’s no going back now, I’ll never give up this power and acceleration. I literally spun my Michelin PSS in third gear today.

 

[Old Guy]

Then I would suggest that the first step would be to check the EACV and clean it and the ports as described in the [MENTION=18194]Honcho[/MENTION] thread. Everything gets more complicated after that.

 

[Jinks]

Then I would suggest that the first step would be to check the EACV and clean it and the ports as described in the @Honcho thread. Everything gets more complicated after that.

Thanks. I’m gonna try this.

 

[mwagner10702]

And . . . are you sure it is not a vacuum leak?

 

[RYU]

It just occured to me that my HKS ECU was tuned extensively for tip-in and off-throttle behavior. This is often where tuners are worth their paycheck IMHO. This was years ago now but I seem to recall a conversation where we discussed there were some off-throttle maps we could manipulate to not make a super lightweight flywheel annoying.

Yes, you won't experience this issue while in gear but your issue could be aggravated by your lightweight flywheel. Check the IACV and check for vacuum leaks. Otherwise, this is likely an ECU tuner thing.

note: vacuum leaks are a pain to find sometimes because in, say.. cracked hoses.. the crack doesn't open up until the engine torque's itself down or shakes around.

 

[Jinks]

And . . . are you sure it is not a vacuum leak?

All vacuum lines are brand new. I do not suspect them to be an issue but as I said, it is strange and intermittent.

 

[JohnWayne]

Have you spoken to a south FL tuner yet?

 

[Jinks]

Have you spoken to a south FL tuner yet?

Not yet. Still searching for one I trust.

 

[Old Guy]

And . . . are you sure it is not a vacuum leak?

The NSX is a MAP sensor based engine control system. Vacuum leaks that admit air to the intake manifold (as opposed to vacuum leaks for something like a control solenoid) just look like more by-pass air to the ECU resulting in a higher idle speed, not low idle speed. However, if idle speed was set up with an engine with a slight leak into the intake manifold and that leak was subsequently fixed, then the engine can have a low idle speed. Particularly if the engine does not use closed loop idle control.

The details of the OEM idle control on the pre drive by wire cars is a little murky to me. I would have thought that Honda would have implemented a closed loop idle control and that the ECU would modulate the position of the EACV to admit air to hit the target idle speed once the TPS indicated that the throttle was closed. I was thinking that perhaps if the valve was gummed up, the valve is slow to respond to the change in control signal since the engine does seem to recover to the correct RPM. Closed loop control should make the idle less susceptible to manifold air leaks up to the point that the valve can not close down any further.

If the EACV is just an on/off type valve with no closed loop control as opposed to a modulating type valve, then air leaks or changes in air leaks will mess the system up big time.

One thing for Jinks / his tuner to consider is that if the ECU is set up with closed loop idle control, the ECU needs to be 'told' that the throttle is closed and its time to implement the idle control loop. This 'throttle closed signal' typically comes from the throttle position sensor. If the throttle position sensor is slightly out of adjustment the position signal may not be crossing the closed threshold all the time. A quick lift of the throttle might allow the sensor to reach closed where as a slow lift may allow the sensor to hang up a bit, particularly if there is any stiction in the throttle cable.

We are into the WAG phase here.

 

[Mac Attack]

The OEM TB incorporates a dashpot kind of design that slows the TB closing when you abruptly lift off the gas. It's mostly for emissions purposes, and I doubt that's your problem. I removed mine about 10 years ago when I modified my TB.

Because it is intermittent, it sounds like the EACV like others have said. Clean it and test.

Otherwise, there are many, many idle parameters to adjust in AEMTuner that you need to experiment with. Like Regan said, this is where a good tuner comes in. Here's a screenshot of one of my files I have with the various idle parameters to show you all the things going on.

Tuning at WOT is simple, but it took me a long time driving around town, datalogging, adjusting the various parameters, and then repeating to get good startup, throttle tip-in, idle, and more.

View attachment 151887

 

[Old Guy]

Look at that box on the lower left in the screen print posted by Mac Attack - the one titled Options - idle. The first parameter is Idle On if TP less. The parameter value in Mac Attack's is 3.9% which means that idle control is not engaging until the throttle position sensor drops below 3.9 % of fully open. If you can find the similar value for your car and you can set up the real time display to show the throttle sensor position, it should be a snap to confirm whether a poorly adjusted throttle sensor is the source of your problem. If when you do the slow build in RPM and then lift the throttle to let the speed drop you see that the throttle position is hanging up above the 'Idle On if TP less' value that is programmed into your ECU, then that means that the TPS is incorrectly adjusted or you have something sticky that is stopping the throttle from going to the completely closed position and preventing the ECU from going into closed loop idle control.

If you have confidence in your original tuner I expect that this is probably not your problem because this is a really basic set up item that is easy to do. However, if something happened to the car in transit - then its a possibility. I offer it up as a suggestion just because if you have the real time display, it is a super easy thing to test and then check off the list as not the cause. If you don't have the real time display of parameters set up, then I would suggest going back to checking out the EACV operation as the #1 item.

 

[Jinks]

Thanks guys. I’ll plug in the laptop this week and confirm.

 

[Mac Attack]

Look at that box on the lower left in the screen print posted by Mac Attack - the one titled Options - idle. The first parameter is Idle On if TP less. The parameter value in Mac Attack's is 3.9% which means that idle control is not engaging until the throttle position sensor drops below 3.9 % of fully open. If you can find the similar value for your car and you can set up the real time display to show the throttle sensor position, it should be a snap to confirm whether a poorly adjusted throttle sensor is the source of your problem. If when you do the slow build in RPM and then lift the throttle to let the speed drop you see that the throttle position is hanging up above the 'Idle On if TP less' value that is programmed into your ECU, then that means that the TPS is incorrectly adjusted or you have something sticky that is stopping the throttle from going to the completely closed position and preventing the ECU from going into closed loop idle control.

If you have confidence in your original tuner I expect that this is probably not your problem because this is a really basic set up item that is easy to do. However, if something happened to the car in transit - then its a possibility. I offer it up as a suggestion just because if you have the real time display, it is a super easy thing to test and then check off the list as not the cause. If you don't have the real time display of parameters set up, then I would suggest going back to checking out the EACV operation as the #1 item.

Jinks - Please note that box had been scrolled down as I was going through it. The top two parameters are Idle Feedback Above 400 RPM and Idle Feedback Below 1700 RPM. See if those are consistent with yours.

Years ago I started a thread on Tuning Help and Calibration File Sharing. That never took off unfortunately.

 

[Jinks]

^Got it.

 

[Jinks]

Jinks - Please note that box had been scrolled down as I was going through it. The top two parameters are Idle Feedback Above 400 RPM and Idle Feedback Below 1700 RPM. See if those are consistent with yours.

Years ago I started a thread on Tuning Help and Calibration File Sharing. That never took off unfortunately.

This is what I took screen shots of this morning. It doesn’t look like I have any type of fuel cut protection. But I’m new to the aftermarket ecu so I am not sure I am looking in the correct place. What do you think of these idle parameters?
View attachment 151955

 

[Old Guy]

Do you know what your throttle position is when the engine is idling? It looks like idle control switches off at 3.1% throttle position. If your throttle position is not dropping below 3.1 % when the throttle is closed, then you may not be going into closed loop idle control.

I don't own an AEM so I am not familiar with how the tuner interface is set up. If I were to guess, I would guess that the fuel cut on trailing throttle might be in the Accel setting window. The de accelerate and accelerate settings sometimes get packaged together; but, no guarantees.

Am I reading the curves in the first screen capture correctly - top right of first screen capture - is your ECU set up with a target idle speed of 2600 RPM when the coolant temperature is below 32 F? That seems really, really high, although not related to your current problem.

 

[Jinks]

Do you know what your throttle position is when the engine is idling? It looks like idle control switches off at 3.1% throttle position. If your throttle position is not dropping below 3.1 % when the throttle is closed, then you may not be going into closed loop idle control.

I don't own an AEM so I am not familiar with how the tuner interface is set up. If I were to guess, I would guess that the fuel cut on trailing throttle might be in the Accel setting window. The de accelerate and accelerate settings sometimes get packaged together; but, no guarantees.

Am I reading the curves in the first screen capture correctly - top right of first screen capture - is your ECU set up with a target idle speed of 2600 RPM when the coolant temperature is below 32 F? That seems really, really high, although not related to your current problem.

I think that target of 2600 rpm is for a negative temp of 40 degrees F. You can see the square box in the figure, that is what I idle at at start up. I have a throttle function on my gauge art but I am not sure that will give me throttle position or not.

 

[Jinks]

It’s looking like I need a really good tune so far. There’s a guy up in Orlando that comes recommended. But I need to get more break in miles on the car before I drive a few hours North. If it is something I can fix with a few adjustments and someone can help with that I’m game for it.

 

[tdiggity]

Throwing out another tuning option for you. Science of Speed told me they can do remote debugging. Probably involves FaceTime plus taking over your computer when connected to the aem. Not sure if they’d do it for everyone or people who did initial tune with them, but couldn’t hurt to ask.


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