I was throwing a P1507 code on my 2002 wrx and was searching for a solution on how to fix it. I got alot of non concrete info in a bunch of threads, especially on the neutral switch, where it is, and how to fix it.

First the P1507, Idle control system malfunction. If you are throwing this code you have exactly two places to look at, the IACV(idle air control valve) located on top of the throttle body mounted with two phillips head screws, or you have a faulty neutral switch(apparently pretty common, especially pre-wrx era cars). So, lets pretend your IACV is gummed and gunked up. Remember this is your idle air control valve which means there is a moving piece in there. So you most likely wont be able to just spray it with carb cleaner or soak it in rubbing alcohol to fix it(this is what i tried first). Its hard to describe what the actual moving valve piece looks like, just know there is a moving object in there that is spring loaded...if you push it in it should spring back quickly once released(you can push on it with a flat head screw driver, or anything thin). Mine was returning slowly, on top of that it wasnt returning all the way to its out position. So i filled my IACV up with rubbing alcohol and just kept actuating the valve with my flat head...it finally started to free up and spring quickly and easily back to its fully extended position. This took me 4-5 attempts of putting the IACV on and off the car and testing, and then cleaning some more. Luckily it takes roughly 15-20 secs to install and remove the IACV. *NOTE*-you will have to replace the IACV gasket, the rubber gasket expands after new and doesnt fit again once removing the IACV. I ordered mine from subarugenuieparts, just email them telling them you are looking for an IACV gasket and what model year your car is, they will get you what you need. I think it was like $7.

Next, if you have a faulty neutral switch. First, it is located on the driver side of the transmission towards the rear of the transmission. I found this link that shows it. http://www.surrealmirage.com/subaru/...location07.jpg
You need nothing more then a 3/4 or 19mm, i think, open ended wrench. Jack the car up, unscrew the switch, remove it from the harness(kinda a bitch until you realize how it releases). Plug in the new switch, screw it back into the trans. Again, i ordered mine from subarugenuineparts, it cost $27. Email them, tell them what you need and what year
This should apply most if not all subaru 5spds(NOT auto's, they are different and switches are more expensive), including older legacies and impreza's.

If you are searching and this thread helped, post up. If you have anything to add, lets hear it.

I just wanted to add a note about the NSS. If you have a tactrix cable, you can step into the ECU either using Romraider logger or ecuExplorer and select the neutral position switch. The value should change from 0 to 1 (on to off) as you go into gears and back to neutral. If the values do not change, then your NSS is bad.

If you do not have a cable/logger, you can still manually test this if you have a multimeter. The wire runs into the ecu, and the pin location varies by year. Ecu pinout information can be found at http://www.northursalia.com/modifica...ng/wiring.html Again, you should be looking for a changing voltage (0v in one, 12v in the other) The relativity between ground and 12v varies between some years (some show 12v in gear, some show 12v in neutral) but the idea remains the same.

Also, a note on the IACV, to better clean the assembly, you can remove the stepper motor (which is magnetic btw) from the valve body assembly and clean the drive system that way. I posted in the IACV thread about this, where the bearing assembly can gum up over time as it is not sealed. Soaking it in gasoline or similar solvent and spinning the assembly and swabbing out any buildup can greatly relieve any issues with a sticking IACV.

I'm having a hard time finding a solution to my problem.

I'm from Australia and have a 1998 WRX - EJ20G I believe?

I have the following CEL:

Code 24 - Idle Air Control Solenoid Valve:

Contents of diagnosis: Idle air control valve inoperative. (Abnormal signal produced in monitor circuit.)

Fail-safe Operation: Prevents abnormal engine speed using "fuel cut" in relation to engine speed, vehicle speed and throttle valve position.

The manual also states that there are 8 sensors that need to be working in order for the IAC to work.

These are:

Crankshaft Position Sensor (changed 3 months ago to a second hand one)
Camshaft Position Sensor
Throttle Position Sensor
Engine Coolant Temperature Sensor
Vehicle Speed Sensor 2 (changed to a brand new OEM Subaru one)
Ignition Switch
A/C Switch
Neutral Position Switch (MT) (changed to a brand new OEM Subaru one)

The problem is stated in the service manual, the ECU cuts fuel around 4500rpm.

The car fines fine, power is good until the ECU cuts fuel, the idle is perfect. I don't know what's going on?!

Can anyone please point me in the right direction?

yea but if any of those 8 sensors were bad they throw a code hence they are electrical and tied to the ECU so if one of them was bad you would knw

My car has just thrown the code p1507 and I can't figure out what's wrong.. I checked my nss and its reading propper voltage and I just cleaned my iacv...any help would be great...thanks.

Sorry to dig this up again but can someone tell me if the iavc gaskets are the same for gd turbo and n/a models?

I have a 5-speed 2002 Subaru Outback wagon with 150k on it. Periodically it'd stall when slowing down while downshifting. I would reliably get the CEL every time I'd downshift going downhill. My code reader showed P1507.

I replaced the neutral switch ($30) and that fixed the problem. The switch was pretty easy to install - basically unscrewing the old one from the transmission, disconnecting the electrical plug, then reverse with the new one. Once you're under the car it's a 20 minute job tops. Good luck.

LINK: http://www.porcupine73.com/endwrench...TroubSum04.pdf

Hi guys,
I tested my NSS and got:
Neutral: 4.75V
1st: 0V
2nd: 0V
3rd: 4.75V
4th: 0.03V
5th: 0V
R: 0V

Does that mean the switch is bad? I have the same P1507 code and cleaned the IAC already

Does anyone know if on a 2002 legacy 5spd if the neutral switch is postive or negitive trigger?

Going by the schematics it seems negitive but by the ECU I/O testing sheet it should be positive? So that puts a little confusion into testing

Thanks

I'm throwing the. same code but my idle seems to be fine, but I'm also throwing a p1088 code. Can somebody help me out here?

I had many codes pointing to real issues that I fixed already. Now I am down to one error code only, the dreadful P1507.
I started having this issue after I replace the timing belt and the coil on cylinder#3. I spung the engine like 10 times and made sure the timing marks are exactly where they suppose to be.
Here is what is going on:
I reset the code "using COBB AccessPort ", start the car and let it warm up till it idles at ~1k. I then step on the gas pedal for a bit then off the gas and the rpm hangs at around 2k for maybe 20 seconds then goes down !1k and throws the code P1507 "Idle Control System Malfunction (fail Safe)." It looks like the ECU notices the rpm not returning to normal and take over to bring down.
Things I already did:
- Replaced the IACV(idle air control valve).
- Replace the Neutral Switch "I tested the original and confirmed that it was NOT working".
-I did check for air leaks using the carb cleaner method and also using Smoke Machine Leak Detector "3psi" and found no air leak what so ever.

I have COBB SF intake, Invidia 3" exhaust, and Stage-2 ots Cobb map. I know it needs a real tune, but I had this tune for a while now and the P1507 issue is new.

I really don't know where to go from here.

I had many codes pointing to real issues that I fixed already. Now I am down to one error code only, the dreadful P1507.
I started having this issue after I replace the timing belt and the coil on cylinder#3. I spung the engine like 10 times and made sure the timing marks are exactly where they suppose to be.
Here is what is going on:
I reset the code "using COBB AccessPort ", start the car and let it warm up till it idles at ~1k. I then step on the gas pedal for a bit then off the gas and the rpm hangs at around 2k for maybe 20 seconds then goes down !1k and throws "Idle Control System Malfunction (fail Safe).” It looks like the ECU notices the rpm not returning to normal and take over to bring down.
Things I already did:
- Replaced the IACV(idle air control valve).
- Replace the Neutral Switch "I tested the original and confirmed that it was NOT working".
-I did check for air leaks using the carb cleaner method and also using Smoke Machine Leak Detector “3psi” and found no air leak what so ever.

I have COBB SF intake, Invidia 3" exhaust, and Stage-2 ots Cobb map. I know it needs a real tune, but

I really don’t know where to go from here.

Did you verify the nuetral switch PID in the ECM changes?
Look to see if the throttle plate stop screw is misadjusted. People will mess with it under the misguided idea that it adjusts idle. Back the screw out until the throttle plate binds in the throttle bore then adjust the screw until the point the throttle plate no longer sticks, then tighten locknut and dab locktight on the screw/nut. If it never seems to unstick look for worn throttle shaft/bent plate. Also double check for vacuum leaks.

Had this car for 16 years and never let anyone touch it, and I never touched the idle screw.
I did take the throttle body out and gave it a good clean. Was not horrible but did end up with a back rag from all the carbon deposits that was in there. The throttle plate is fully closed when it is out and it does moves freely. With the throttle plate closed and shinning a flash light from the rear, I see the some light passing through the front, from left center to the bottom, like a crescent share. Is this normal or does it mean that my throttle plate is not centered or out of shape?

Your comment "Did you verify the neutral switch PID in the ECM changes?", how do I check for that? Is this a log I add and monitor using my Cobb AccessPort?

Is the throttle cable adjusted too tight? There should be a small amount of slack in the cable at idle so that the throttle plate will close.

Did you use a new gasket when you reinstalled the throttle body? Did you overtorque the throttle body (22 Nm)?

Did you use a new gasket on idle valve and torque to 2.8 Nm?

Unless you dissassembled the throttle plate from the shaft or bent the plate then it should be in the same position before you cleaned.

Look at the PIDS on your Access Port, there should be one for the neutral switch. Verify the ECM sees that value change when shifting from neutral to in a gear.

Small slack in the cable at idle is still there.

I used new gasket when you reinstalled the throttle body and did torque it to spec.

I used new gasket on idle valve and torque and torqued it to spec.

Throttle body is in the same position before you cleaned. I did not disassemble.

Other things I did already:
- idle relearn procedure
- Fuel pressure test: While the car is running, the pressure is up where it should be with minimal movement even when I rev it. It does go down after I shut off the engine. I assume that is normal that it can't maintain pressure for too long, right?
-Fuel Pressure Regulator: No sign of fuel present in the Regulator's Vacuum Line.
-Cleaned and tested the the passenger side fuel injectors while replacing the head cover gasket. Of course replaced all O-rings and filter before I plugged them back in. They were working fine when I tested them before cleaning.

As I mentioned before, I did use a multimeter and found the old Neutral Switch not working and used the same test and made sure the new one is good before I installed it.

So, next is to plug in my AccessPort and look at the PIDS.

I was in the middle of replacing the clutch master cylinder and the weather got too cold for me to work on the car. Finally, it is a warm day. So, finished bleeding the clutch and installed the tmic. So, back to it!

The TPS is working. I measured the current at idle and it was .57 and went up to 3.76 and back to .57 without any spikes or drops "battery was bit under 12v when I took the reading". I also saw the same readings using the AccessPort while the car is running.

Gear Position Sensor is working. Shows 6 when in neutral and 1 when in any gear.

The idle issue is still there. RPMs creeps up, ecu throws codes P0507 and P1507. ECU takes over and brings it back to about 1100 and the idle goes up and down between 1185 and 1200.

I replaced the MAF since I did find some online posts and YouTube videos about it getting bad but not throwing any codes. Before I replace the MAF, the car stumbles severely when I step on the gas and not at any specific rpm. After replacing the MAF, she revs almost great and not a single stumble whatsoever. That is a huge win!!! but also tells me that the stumbles were unrelated to the Neutral Switch and the TPS.

I took the car for a short drive. When I stop at a stop sign with the clutch all in, I notice the rpm is high near 2k then drops to normal after a second or two. I think the ecu is catching it and making the correction.


I reviewed all logs while the car is running at idle "and recorded it, see link below":


A/F Correction 1: 2.2/10.2, now that looks like a big variance
A/F Sens 1 Ration: goes from 15.5/23.1
Battery is +13 volt. I did test the charge while the car is running to make sure there is voltage drops.
Boost: -9.0/-8.9
CL Fuel Target: 13.8/14.7. Is this normal?
Closed Loop Sw.: 0/1.
Comm Fuel Final and Map: 14.7/14.7
Idle Mode Sw.: 1/1
Ignition Timing: 7.5/20.0
Ing. Duty Cycle: 0/7
Inj. PW (No Lat): 1.5/1.9
Inj. PW (w/Lat): 0.0/2.3
Neutral Pos. Sw.: 1 when in neutral, and 0 when in any gear
TD Boost Error: 7.5/8.3 psi
TPS Voltage: .5/.8. When I give it throttle, it goes up to .9 then the AP screen flashes!

Can someone tell me what else I might be missing?

After replacing the MAF, did you reset the ECU? Clearing codes, disconnect battery, etc., quite a few ways to clear ECU learning of a bad part.
Yes, it will crank longer the first time as the ECU figures out what hard parts are doing.

I cleared the error codes, key off for a few minutes, then key on and start the car. No error codes. The idle started bit high and tapered down to a normal level after the engine got worm "normal expected behavior". Then the idle started to creep up slowly. I stepped on the gas pedal and off. The car revved nicely "no stumble" but the idle went down to 2k for a few seconds then went down to normal ~1k and the error codes popped up again.

Guys, I am still stuck and need your help!!!
Reviewing the log in the video posted above, the "Gear Position" shows number 6 when in neutral and 1 when in any other gear "1-5 and reverse". Is that normal or should it indicate the correct gear number "1,2,3,...etc."?
Is there another sensor that tells the ECU which gear the car is in?

As mentioned above, I did replace the "Neutral Safety Switch" which is located on the transmission. But from the name, I imagine it's job is to tell the ECU if the car is in neutral or not and not which gear the transmission is in, right?

That is a simple on/off value - don't know why Cobb puts some silly value to it. The only way Subaru derives gear position information on manual transmissions is correlation between engine RPM and road speed. Only much later models display gear position data. Gear value CANNOT be determined sitting still, only in gear/out of gear.

What happens if you unplug the MAF sensor and start the car (beside the check engine light and code for MAF & IAT)?

Here are some values to check.

Neutral position switch = 12 volts (on) in Neutral, 0 volts (off) in ANY gear.

TPS = Key on engine off: fully closed 0.2 to 1.0 volts. Fully open 4.2 to 4.7 volts. Smoothly increasing voltage while slowly opening throttle.

Power steering switch/engine running = no steering input battery voltage, steering input 0 volts.

Your idle AFR should be around 14.7 If you have a continous value over 15 then you may have a vacuum leak or fault A/F sensor. Your fuel trim values will also be pushing towards the positive side if you have a vacuum leak.