Tonys96Cobra - Idle Jump and Codes

Tonys96Cobra · May 12, 2022

First post in 11 years.... Finally back in the game, yay for me I guess.

89GT, original 5 speed car, stock motor. A/C was removed by some nimrod in the past, o2 sensors are still in place. Smog pump has been removed

Car idles at 800-900 RPM as long as the clutch is depressed all the way. Soon as you let the clutch out, idle jumps to 2200 and stays there forever.

Things I've done: Clean MAF and TB, replace TPS and IAC. Checked and cleaned the 10 pins.

Car has codes 22, 67, and 85. No CEL.

Codes were pulled with the HVAC turned to OFF, trans in neutral, clutch fully depressed, also pulled codes with the clutch let out, code 67 every time.

NSS is working, car won't start unless clutch is depressed.

85 is probably because he removed the smog stuff, 22 shouldn't have anything to do with this specific issue?

I ran through the checklist, didn't see anything regarding this specific issue, most seemed to deal with RPM dropping when the clutch is in.

Any ideas for an old man just getting back into it???

EDIT

Tried a couple more things.

Disconnected the NSS at the clutch, no change whatsoever.

Disconnected the switch at the transmission, now the car idles great with the clutch out, and drops around 100-200 RPM with the clutch depressed.

AUSTEXLX · May 12, 2022

I'll be honest, I'm totally guessing here. However, mechanically, the pedal box may be a culprit? Perhaps there's something binding the throttle pedal and the clutch cable quadrant? Is it worth checking that out? Maybe it is a crazy idea, but maybe not. Would love to hear how it works out.

ReefBlueGT · May 12, 2022

Sounds to me like it could be a malfunctioning speed sensor or maybe the TPS but I know you just replaced it. The computer is keeping the idle high with the clutch out so that the car doesn't stall, thinking that the car is moving even though it's standing still.
One other thing, have you reset the base idle by disconnecting the IAC and SPOUT? Then disconnected the battery to let the computer and everything discharge for 10-20 minutes so the stored settings/adjustments get cleared? There's another thread with more of the method, but it boils down to doing the above, then starting the engine and running at idle with NO electrical loads for two minutes; turning it OFF for two minutes; then starting and running another two minutes with full electrical load (lights, AC, etc). Supposedly retrains the computer on how the engine should idle with and without load.

Tonys96Cobra · May 12, 2022

ReefBlueGT said:
Sounds to me like it could be a malfunctioning speed sensor or maybe the TPS but I know you just replaced it. The computer is keeping the idle high with the clutch out so that the car doesn't stall, thinking that the car is moving even though it's standing still.
One other thing, have you reset the base idle by disconnecting the IAC and SPOUT? Then disconnected the battery to let the computer and everything discharge for 10-20 minutes so the stored settings/adjustments get cleared? There's another thread with more of the method, but it boils down to doing the above, then starting the engine and running at idle with NO electrical loads for two minutes; turning it OFF for two minutes; then starting and running another two minutes with full electrical load (lights, AC, etc). Supposedly retrains the computer on how the engine should idle with and without load.

Will do the timing here shortly, thanks for the suggestion. I can't put an AC load on it, since its gone, but can do headlights I guess. The car is kind of stripped right now, going in for paint on Monday. Trying to get this sorted out before I pull the motor and put it back in with some mild mods.

ReefBlueGT · May 12, 2022

Definitely search around and do some reading here in your spare time - I've learned a lot, and had never been mechanically inclined until I got this car a few years ago. If you're gonna be doing mods anyways, you might not want to dwell too much on this issue since, depending on what mods you do in the future, that could lead to other things you'll have to tweak. Oh, and don't be afraid to start a new thread with any problems you have - I think people jump on it a little more quickly, and can then help you get on the right path. I've found that searching google with stangnet.com and whatever info you're looking for can sometimes work a little better than the search box on the website, and get you to a relevant thread quicker.

Noobz347 · May 12, 2022

I've moved this issue to its own thread. Make sure you subscribe to this thread if you're following.

General karthief · May 12, 2022

Help me create the "Surging Idle Checklist"

Updated 26-Oct-2019 to clarify creeping idle RPM increase as the car is being driven. Many of you are familiar with the "Cranks OK, but No Start Checklist for Fuel Injected Mustangs" checklist and the No Crank Checklist. They are very effective in finding and eliminating the problems by use of...

forums.stangnet.com

Fix any issues you have before you add modifications, adding modifications to an ill operating engine only makes it more difficult to fix.

Noobz347 · May 12, 2022

General karthief said:
Help me create the "Surging Idle Checklist"

Updated 26-Oct-2019 to clarify creeping idle RPM increase as the car is being driven. Many of you are familiar with the "Cranks OK, but No Start Checklist for Fuel Injected Mustangs" checklist and the No Crank Checklist. They are very effective in finding and eliminating the problems by use of...

forums.stangnet.com

Fix any issues you have before you add modifications, adding modifications to an ill operating engine only makes it more difficult to fix.

Hehe... That thread is where I found this so he knows about it.

Dan02gt · May 12, 2022

I would suspect that the NSS switch on the trans is your issue. The NSS system functions by having the clutch switch and trans switch in parallel and open when the clutch is out and car is in gear. This tells the computer that the car is in gear and moving and to initiate the dashpots anti stall feature. The anti stall being activated with no load will cause the idle to be around 2000 RPMs. I had the same issue and it turned out someone had installed a reverse light switch place of the NSS switch and some of my wiring was bad so the NSS circuit was not seeing the full voltage.

Tonys96Cobra · May 12, 2022

Dan02gt said:
I would suspect that the NSS switch on the trans is your issue. The NSS system functions by having the clutch switch and trans switch in parallel and open when the clutch is out and car is in gear. This tells the computer that the car is in gear and moving and to initiate the dashpots anti stall feature. The anti stall being activated with no load will cause the idle to be around 2000 RPMs. I had the same issue and it turned out someone had installed a reverse light switch place of the NSS switch and some of my wiring was bad so the NSS circuit was not seeing the full voltage.

That would make sense, the car idles great with the switch unplugged. No to find one, didn't see one on Rock auto.
Edit, looks like LMR has them. Thanks

KRUISR · May 12, 2022

Tonys96Cobra said:
Car idles at 800-900 RPM as long as the clutch is depressed all the way. Soon as you let the clutch out, idle jumps to 2200 and stays there forever.

What does your car idle at with IAC and SPOUT unplugged? Should be in the 500-650 range.

Mustang5L5 · May 12, 2022

Dan02gt said:
I would suspect that the NSS switch on the trans is your issue. The NSS system functions by having the clutch switch and trans switch in parallel and open when the clutch is out and car is in gear. This tells the computer that the car is in gear and moving and to initiate the dashpots anti stall feature. The anti stall being activated with no load will cause the idle to be around 2000 RPMs. I had the same issue and it turned out someone had installed a reverse light switch place of the NSS switch and some of my wiring was bad so the NSS circuit was not seeing the full voltage.

This is my guess as well, especially with a code 67 present. However pressing the clutch in should clear that. So I think there’s and issue there with wiring.

But to be clear, the switch on top of the t5 is the NGS. Nuetral GEAR switch. It tells the ECU of the trans is in gear or not and is in parallel with the clutch switch.

There is no nuetral safety switch on a 5-spd Mustang. It’s jumped out on the reverse harness and not used. These cars only use a clutch safety to prevent in-gear starting.

Calling it an NSS gets confusing because the NSS and NGS have different functions.

Tonys96Cobra · May 12, 2022

KRUISR said:
What does your car idle at with IAC and SPOUT unplugged? Should be in the 500-650 range.

It was around there, I set the base timing to 10, it was only around 4. Car idles great now with the NGS switch unplugged. Definitely want to figure out why though, going to want the car running right when we get the AC and everything back on.

Dan02gt · May 12, 2022

Mustang5L5 said:
This is my guess as well, especially with a code 67 present. However pressing the clutch in should clear that. So I think there’s and issue there with wiring.

But to be clear, the switch on top of the t5 is the NGS. Nuetral GEAR switch. It tells the ECU of the trans is in gear or not and is in parallel with the clutch switch.

There is no nuetral safety switch on a 5-spd Mustang. It’s jumped out on the reverse harness and not used. These cars only use a clutch safety to prevent in-gear starting.

Calling it an NSS gets confusing because the NSS and NGS have different functions.

I was referring to NSS as being neutral sensing system with the clutch switch and transmission switch being part of that system. Sorry if it was confusing.

Tonys96Cobra · May 13, 2022

We'll, ordered a switch from lmr, but won't be able to install for a while, car is going in for paint on Monday. I'll update this when I get it figured out so someone 10 years down the road can benefit.

TomOsiris · Jun 21, 2022

Tonys96Cobra said:
We'll, ordered a switch from lmr, but won't be able to install for a while, car is going in for paint on Monday. I'll update this when I get it figured out so someone 10 years down the road can benefit.

I also have a mystery code 67, did a new neutral sensing/gear switch fix your issue?

Tonys96Cobra · Jun 25, 2022

TomOsiris said:
I also have a mystery code 67, did a new neutral sensing/gear switch fix your issue?

Haven't installed the new switch yet, car is still at the paint shop for about another month

Tonys96Cobra · Oct 28, 2022

Whelp, as far as a progress update, got the car back from paint. Guy did a a55 job, wouldn't fix it, then literally closed up shop and disappeared. Going to have to live with it, can't swing any more money for paint.

Got the 5 lug and rear discs done, new springs/shocks and whatnot.

Here's a pic from the best possible angle, looks sick driving through the 'hood', just don't get too close lol

The day I got it., May of this year.

As she sits now.

Tonys96Cobra · Oct 28, 2022

Back on topic. Replaced the NGS (neutral gear switch) today, she still idles at 2k, but will drop back to 900 when the clutch is depressed. Any ideas?

Mustang5L5 · Oct 28, 2022

Go under the dash to the clutch pedal. There are two plugs on the clutch switch. Remove the clear one and put a 5amp blade fuse in it. This jumps it out, like having the clutch pedal pressed in all the time.

This is a temp fix, but hopefully solves the 2k hanging idle.

From here, I would troubleshoot the wiring from the NGS to the ECU. It’s pin 30 and pin 46.

Rather than pull the ECU. With the car off, stick a digital multimeter into the above clear plug on each pin and check for continuity as you move the shifter from gear to nuetral.

Tonys96Cobra - Idle Jump and Codes

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