For a while now I have been chasing a runaway idle and hang throttle.

I do not drive the car very often. When the weather is nice, but basically and mainly, it is a garage queen.

I posted long ago on this forum as well as others and got a lot of response of people stating they had a similar issue or PM's asking if I found the issue, but nothing solid.

I have not, and as the title states, I have a run away idle and hanging throttle.

I never popped a code or light up until recently for P0507 "Idle higher than expected".

It does not surge or seek, just sticks and or slowly increases, sometimes to redline...

Driving normally, put in the clutch off the gas and on the brake to stop at a light, the throttle hangs at whatever RPM you where cruising at and sometime slowly increases like I said.

Before you say intake leak, I have looked and looked more than you could imagine. Carb cleaner trick, replaced any suspect lines, capped, pinched, tightened, you name it. Nothing, and like I said, its not all the time.

The strangest thing is, if I pull up on the accelerator pedal with the top of my foot, bending the armature, the RPM's drop...

So, I performed the accelerator pedal position relearn. When I think its fixed, it does it again.

Given the above, I figured it was a bad pedal sensor, so I replaced it with a used pedal and performed all the resets/relearns. All seemed well for a few, but again, hardly drive the thing.

Well, its doing it again and here I am posting another thread in hopes of some guidance.

Tonight, while it was hanging at 2.5k in the driveway, I went under the dash and wiggled the connector on the pedal... The RPM's increased and dropped.

Thinking I had a a broken wire or recessed pin, I pulled the connector, removed the wrap and inspected.

I did not see anything obvious, so I reconnected and started the car.

It was now at 4k, so I lift up of the pedal with my foot and RPM's drop to about 900, let off and back to around 4k it went.

Push the bracket/tab the sensor is mounted to on the pedal assembly towards the driver side, RPM's increase, push towards the passenger side, RPM's increase.

Looking at the sensor while bending left and right the sensor rotates very slightly. Pulling up on the pedal as well rotated the armature slightly as well.

Bad pedal again?..

The pedal was used after all, but same exact situation as the other? The sensors is indexed and the screws are marked in the mount.

Its been so long, I dont have a clue where the original pedal assembly is at, and I removed the sensor as well.

Do you think something is possibly burning up the sensor? Maybe it was never really "fixed" in the first place...

Is it safe to assume I have at least isolated the problem?

Any ideas or suggestions?


Info:

2006
Boosted (Vortech tuner kit)
ID725's
Walbro
UpRev GT MAF
Motordyne MREV2 w/ spacer
Stillen headers, Z1 test pipes, Borla cat back.
HKS ignition amp
UpRev tuned
(Koyo radiator, Stillen oil pan, DIY oil cooler (Mocal and Earls), AGP baffled oil catch can and custom blower intake with AN bung and fitting for PCV).

 

From what you said it does sound like it's isolated at the pedal somewhere. If you use your hand to depress the pedal and let it "spring back up" does it slap up very quickly or does it feel like the hinge or linkage is binding up on something?

Have you thoroughly inspected the area for anything else that could be impinging the movement of the pedal?

Remove the pedal and perform the test procedure for the switch as listed in the FSM with a digital multimeter and 3x AA batteries in series (battery holder from Amazon/eBay/kids toys) to provide voltage.

Other things worth checking, idle air control valve function test as well as cleaning it's passageway, visually confirm proper operation of the throttle motor in relation to the pedal movement. Also if the pedal switch goes through the cabin super multiple junction I would separate it and look for corrosion (not sure if it does, check the fsm wiring diagram).

It is definitely possible you got a bad pedal switch though, especially considering it was used however to have the EXACT SAME problem sounds a little suspicious, testing it is the right call.

Edit: Nice looking car!

 

Just thought of something else also, OBD2 scan and check what % throttle is actually being transmitted to the ECU when the RPM's start to run away.

 

Appreciate the reply!

I did check the spring tension/snap back. All good there.

Nothing is obstructing the mechanism in any way. (I thought the same thing)

I am familiar with wiring diagrams and multimeters, so any test I can and will perform. (I wasn't aware of the battery trick)

I am working 12's right now, so I only get to mess with it at night for an hour or so.

Do G's and Z's have IACV's and if so, is it incorporated in the throttle-body?

I will hook up my laptop and see the relation to APP and TPS.

As I understand it it is roughly a 0-5v signal correct?

I saw the junction last night, so I'll take a look.

Also, I will inspect and clean the throttle body as well as the MAF whenever I have the time.

Pretty crazy and embarrassing reving to redline next to a minivan at a light.

Thank you for the guidance and kind words. A lot of time and $ as your aware. The only thing I skimpt on was the rims. The roads here are HORRIBLE. I also want to go back down to 19's.

 

Well I was wrong about the idle air control valve, this engine doesn't use one and instead prefers a fancy math trick calculation with the ECU.
The APP has two switches, you should be able to see them both with your laptop:

ACTUAL MEASURED VOLTAGE
APP1 Pedal released 0.5 - 1.0v, fully depressed 3.9 - 4.7v
APP2 Pedal released 0.15 - 0.6v, fully depressed 1.95 - 2.4v

VOLTAGE READ FROM THE ECU (What you will see with your laptop)
APP1 Pedal released 0.5 - 1.0v, fully depressed 4.0 - 4.8v
APP2 Pedal released 0.3 - 1.2v, fully depressed 3.9 - 4.8v

Basically a high and low range switch and the ECU does the math from there and recalculates APP2

Something else that I was thinking is a possible malfunction with the cruise control system? However it all runs through the ECU so there's a chance your ECU is about to give up the ghost, dunno?

Does your boost spike normally when it's doing this? What about fuel pressure as well? (If you have gauges for those). Runaway fuel pressure (blockage in the return system) COULD cause the engine to exceed rpm due to increased demand for air (ECU trying to maintain A/F ratio and having to increase air volume).

If you can reproduce the issue while logging I'm sure it would be OBVIOUS what sensor is sending abnormal data.

 

Thanks again.

I do not have a boost spike, it remains in vac. -18 to -20 usuall depending on RPM.

I do have a direct FP gauge under the hood. I'll take a look, but when I installed the pump a few years ago, I forgot to do the swirl jet mod, but pulled it and performed it. I want to say it's @ 56ish. I'll look again when it's running and post a exact reading and pic.

According to Google, the shop manual for the 350z states fuel pressure should be "approximately 51psi" although I see some are 55 @ idle.

I started it today when I got home and logged, .48v depressed and 4.6v @ WOT.

I do have WB gauges for both banks and don't see a huge flux/fight to hit target AFR's.

Obviously it wasn't doing it today, but I will try and get it to occur again and check all the above again.

Can't mess with it now, neighbors would be upset. Lol!

Again it's an 06', but only has 59k.

 

Still 56 @ idle, but I can't get it to do it again... Go figure.

 

I haven't been able to get it to do it again, but it does seem to idle a tad high as well as not drop RPM as fast as Id like.

I picked up a new, used pedal along and a reman'd throttle body along with some MAF cleaner for good measure.

I'm actually am going to wait for it to do it again before changing any parts as I am curious to see what is going on value wise.