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Runaway idle /EFI/ throttle by wire


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Joeb1983
New User

May 20, 2016, 4:24 PM

Post #1 of 11 (921 views)
Runaway idle /EFI/ throttle by wire Sign In

2006 Infiniti G35 coupe. (350z)
3.5l, VQ35DE revup
6 speed manual
58k

Engine RPM rising with no accelerator pedal input.

Lift off gas, put in clutch, RPM will hang and then rise to 4, 5, 6, 7k...

If I pull up on the accelerator pedal hard, bending the armature RPM's will drop.

To me I thought it was a bad accelerator pedal position sensor...

I replaced the entire pedal assembly given you can't just purchase the sensor alone and seeing how the sensor is indexed in the bracket/mount.

Drove the car for about 5 minutes after instal, seemed fine and I thought all was well, so I drove it to work.

After around 30 miles stopping at a red light RPM's started rising again...

Pull up HARD on the (new) pedal they drop...

It will slowly rise to the limiter if I let it...

Any ideas?

MAF is fairly new. Less than 3k.


(This post was edited by Joeb1983 on May 20, 2016, 4:24 PM)


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

May 20, 2016, 4:46 PM

Post #2 of 11 (906 views)
Re: Runaway idle /EFI/ throttle by wire Sign In

If you haven't done it already, have the computer scanned for codes.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Joeb1983
New User

May 20, 2016, 4:48 PM

Post #3 of 11 (904 views)
Re: Runaway idle /EFI/ throttle by wire Sign In

I have a scan tool and there are no current or pending codes unfortunately... (should have listed that)

Appreciate the reply.

*** I also should mention I have performed the accelerator pedal position reset as well. ***

No fix.

Also, RPM is not searching nor erratic. It's a smooth increase just as if I was slowly pressing down on the pedal.

Pins on both connector arnd sensor are not receased, bent or broken.

The thing that stumps me is why does the RPM drop if I pull up HARD on both the old and new pedal assemblies.

They both are at their mechanical stops... Plus, again this is a brand new assembly doing the exact thing, so obviously that was not the issue.


(This post was edited by Joeb1983 on May 20, 2016, 5:11 PM)


kev2
Veteran
kev2 profile image

May 21, 2016, 7:14 AM

Post #4 of 11 (867 views)
Re: Runaway idle /EFI/ throttle by wire Sign In

my first thoughts....
Is your 'scanner' up to the job? these codes will likely be so called manufacturers specific.
Also will scanner allow you to view 'live' data - ?
important- vehicle is STOCK ?
I will look at TSB's and reflashes awaiting answers...


Discretesignals
Ultimate Carjunky / Moderator
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May 21, 2016, 7:20 AM

Post #5 of 11 (866 views)
Re: Runaway idle /EFI/ throttle by wire Sign In

Does your scan tool have data stream capabilities? If so, you should graph APP 1 volts, APP2 volts, TPS 1 volts, TPS 2 volts, actual engine rpm, and desired engine rpm. See what those pids are doing when your problem is occurring. Maybe that information can paint a better picture.

Probably would also be a good idea to scan for codes on the manufacture side. Sometimes manufacture codes don't show up on the OBD2 side. You need a enhanced scan or the factory scan tool to get more information.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


Joeb1983
New User

May 21, 2016, 9:33 AM

Post #6 of 11 (857 views)
Re: Runaway idle /EFI/ throttle by wire Sign In

My scan tool has the ability to view live data.

I also have tuning software that has all the features of consult II. (However I can't get it to open after upgrading to Windows 10)

I guess that gives away the car is not stock...

This is where I usually lose peoples help or go on a wild rabbit chases.

Given its been fine up until now I figured it had to be a simple component failure unrelated to the modifications given all had been completely fine up until now.

Here is a condensed list of mods. Any specifics feel free to ask if your still with me. Haha!

Vortech supercharger
Walbro drop in pump (255lph)
Injector Dynamics 725cc fuel injectors.
UpRev GT MAF (recalibrated OEM)
Full exhaust (headers [dealer installed], cats and exhaust)
Jim Wolf technologies clutch and fly (dealer installed)
UpRev Osiris tuning software (unlocks and re-flashes oem ecu)
Very conservative dyno tune from a world renowned tuner.

Viewing live data I don't see anything crazy. Ignition advance follows RPM, MAF is not erratic, coolant temp, IAT all steady and nothing high or low.

I can't view APP only TPS and It seems to correlate. It's a gradual rise in RPM; maybe 1k per 1.5 - 2 seconds so it's not a huge increase.

I wish my software worked. I can log no problem.

I see no fluctuations with vac and I have no boost leaks


(This post was edited by Joeb1983 on May 21, 2016, 9:44 AM)


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

May 21, 2016, 10:15 AM

Post #7 of 11 (850 views)
Re: Runaway idle /EFI/ throttle by wire Sign In


Quote
This is where I usually lose peoples help or go on a wild rabbit chases.


That is perfectly understandable. Most of the professionals in the auto repair industry don't get too many modern modified (electrically and mechanically) vehicles in the shop or even want to deal with them. Modifications open up another world of possible problems. Once you start getting into software changes and other mods, the factory repair information becomes useless.

I know that in factory software, the PCM is monitoring the correlation between sensors to be sure they are in agreement. If the PCM sees an increase in idle speed or rpm, but doesn't see APP voltage changes, it should go into reduced power mode and either fix the throttle position or kill injectors. It should also flag codes. If it sees sensor correlation errors or sensor circuit issues it should do the same thing. There has to be redundancy for safety. It is how the factory software is written. When software is altered or modified, it is possible those parameters for TAC issues are not included or altered so they don't perform the same way? Hard to say without knowing exactly how the modified software is written.

If it was factory software and you had no error codes or reduced power messages, I'd say yes, the PCM is seeing an APP1 and 2 change for some reason and bringing up engine speed. Then you need to find out what is causing the voltage changes for APP inputs. Really don't know why pulling on the accelerator pedal causes the engine to come back down, unless you're changing the APP voltage input voltages into something the PCM software doesn't usually see or recognize.

If you had a 4 channel lab scope you could also scope the TPS and APP sensors and actually see if the throttle is opening and causing the higher idle or if there is something else causing the engine to idle up. Really need some data from those sensors. Probably would also be interesting to see what the injector pulse width is doing if you don't see changes in TPS voltages or throttle percentage during the idle up concern. You also have to know what those voltages should be normally, of course. Need a baseline to work from.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on May 21, 2016, 10:18 AM)


kev2
Veteran
kev2 profile image

May 21, 2016, 10:39 AM

Post #8 of 11 (841 views)
Re: Runaway idle /EFI/ throttle by wire Sign In

"Given its been fine up until now I figured it had to be a simple component failure unrelated to the modifications given all had been completely fine up until now"
you are discounting that a modified component has failed- They are the most LIKELY to fail.


getting the scanner working is key, I wonder if the throttle plate is actually moving OR something causing hi RPM,
look at the throttle control motor - is the circuit ECM to motor actuator , open, shorted to power, look at trouble trees p2100 and up as that is the fly be wire system wire colors ECM pinouts, tests etc....


GTG first susprct is always aftermarket


Joeb1983
New User

May 21, 2016, 10:48 AM

Post #9 of 11 (838 views)
Re: Runaway idle /EFI/ throttle by wire Sign In

I see what your saying, I just have a feeling its not the blower, fuel system or exhaust causing the issue.

I'm not even in boost when it ramps up.

I have wide bands and I don't see any fluctuation or any lean or rich conditions from target AFR's.

I'm un-installing and re-installing the software now.


kev2
Veteran
kev2 profile image

May 21, 2016, 11:02 AM

Post #10 of 11 (832 views)
Re: Runaway idle /EFI/ throttle by wire Sign In

sorry I had to go... What I was thinking was


Because the ECM sees no conflict between APP and TPS I question if the throttle plate is really moving. and something else is causing RPM.


The RPM ranging up may require several incidents to set codes they are NOT 1 failure type.
I think your pulling up on throttle is causing a out of range issue and the ECM defaults - the issue causing high RPM is no longer present, the one time pulling on APP assy would not code and you return to 'normal' .


have you looked at MAF - is it gong up as RPM goes up?
With a blower positive manifold pressure how do you handle EVAP purge, and similar functions?


(This post was edited by kev2 on May 21, 2016, 11:06 AM)


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

May 21, 2016, 11:23 AM

Post #11 of 11 (830 views)
Re: Runaway idle /EFI/ throttle by wire Sign In

Just like with any drive-ability problem, the first thing is to identify what is causing the concern. You need to start here first before guessing and swapping things. Collecting data from suspected systems, doing visual inspections, and interpreting data to figure out what is going on is important.

Once you identify the what, then proceed to figure out why. Once you isolate the why and repair it, then figure out why the why occurred, so it doesn't happen again.

Sometimes you can get caught up in rabbit holes diagnosing stuff. That is where thinking outside the box is helpful. If you see things in data or reactions by something that don't make any sense, sometimes resets can fix the issue. I've run into a few vehicles that doing a reset by disconnecting the battery, touching the terminals together, and turning on the ignition for a period of time, actually corrected the anomalies. Somewhere in software or logic functions the PCM gets caught up in loops and does strange things. Why this happens I don't have a clue. Fully powering down the PCM, just like your PC, can bring things back into order sometimes. Recognizing the weird things that are unusual come with experience. Sometimes connecting a certain brand of scan tool or device to the OBD2 connector or even accessing certain modules can cause all kind of weird things to happen.

Our shop uses an Autel scanner and the other day I connected into 06 Hyundai Santa Fe. When I did a full system scan the engine shut off. I noticed the engine shut off when the scanner was getting codes from the immobilizer system. I didn't condemn the vehicle. I suspected it had something to do with how the scanner communicated with the module. It was repeatable of course. Just so many variables to deal with on these vehicles and it gets worse with modifications.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on May 21, 2016, 11:27 AM)






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