Idle Problem
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This is a discussion on Idle Problem within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; About half the time I shift out of gear, my RPM's drop dangerously low like it is about to die, ...

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    Idle Problem

    About half the time I shift out of gear, my RPM's drop dangerously low like it is about to die, then catches itself at the last minute. Is this a neutral safety switch issue? If so, how do I get to the switch without dropping my tranny? Also it seems like half the time my lights dim a bit according to my driving. I bought the works for a DIY grounding kit, but is this a charging issue or are all these problems relative?
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    Registered User AsILayDying's Avatar
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    I have an 04' and my headlights would dim when I hit the brakes. It was the battery, half dead so the alternator was working 2 times harder to keep power. Good luck with the idle issue.
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    Moderator Donkey's Avatar
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    Quote Originally Posted by itWRXjustfine View Post
    About half the time I shift out of gear, my RPM's drop dangerously low like it is about to die, then catches itself at the last minute. Is this a neutral safety switch issue? If so, how do I get to the switch without dropping my tranny?
    Do you have a aftermarket BOV? Try cleaning the IAC valve and MAF sensor first. Don't know how the switch would effect idle.

    Quote Originally Posted by itWRXjustfine
    Also it seems like half the time my lights dim a bit according to my driving. I bought the works for a DIY grounding kit, but is this a charging issue or are all these problems relative?
    Load test the battery,clean both terminal ends of the cables,test the alternator (multimeter),clean the factory grounds,check the belt tension...... You lights are going to dim especially if your sitting at idle and you radiator fans turn on while you have the heater on with your sound system cranking. I put a diode in the alt reference line so I now see 1/2 volt more through out the system. Not to mention I snagged a used alt from a STi. They are 90A compared to the 2.0L stock 75A.
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    Registered User Sarra's Avatar
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    For the idle dropping to nearly 0 then popping back up to normal idle, there could be two causes to this.

    First is IAC. Easy fix is to get some Carb clean, a new IAC gasket from Subaru ($4.82 or so), pull the IAC, and clean it with carb clean. If that doesn't do the job, then you probably have a dirty throttle body.

    Use more of your trusty carb clean, and get a toothbrush (one you will never, ever want to use in your mouth again). Pull your IC, open your throttle, and spray the throttle plate with carb clean. Then scrub it with the brush. Also scrub the bore where the plate closes. After all of the PCV crap is cleaned off the throttle body, put the intercooler back on, and see if your idle is happier.

    Most likely, it will idle high at first, and come down slowly to normal idle. After driving for a day, it should relearn idle and be normal again.

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    Moderator Donkey's Avatar
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    Carb cleaner kills O2 sensors and MAP sensors. It's best to use throttlebody cleaner as it is O2 sensor and MAP sensor safe.
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    The reason why I ask about the NSS is because I have seen in other posts and I bought the switch in case I had to change it, the NSS is just a open/close button connected to a sensor. Every time you come out of gear or shift the button on the switch tells the ECU to revert to idle. The service manual says that a faulty NSS will result in erroneous idle. That and I have thrown the CEL a couple times. I have done a MAF cleaning and will do an IACV and TB cleaning here soon.

    Slightly off topic but how high should my cold start idle be?
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    Registered User Sarra's Avatar
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    I logged my IAC while driving, due to a thread on NASIOC.

    On my car, my IAC opens to 99% when in open loop (flooring it). Then, when I let off, it goes 'oh crap!' and closes, but not quick enough, which causes an annoying surge right after I let off the throttle.

    Anyway, cold start, the car should start, hold idle at around 1500 RPM, and gradually as the coolant temp increases, decrease the idle speed to 750ish RPM's. IF you start the car cold, it hops up to 1500 RPM, sits there for a few seconds, then drops to 850-900 RPM, your NSS is open. Basically, it thinks you are stepping on the clutch to put it in gear, so it nixes the cold start routine to help with driving.

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    Alright IACV sounds like the culprit. Does anyone know how to swap my NSS with out dropping the tranny. The CEL for it comes on every now and then and I already have the switch.
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    He simply abides. SD_GR's Avatar
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    You have thrown a CEL for a neutral safety switch?! Has your geabox ever been removed? Is the harness on the "top" of the gearbox (as luck would have it, "under" the IC so hard to check relatively) connected well?

    Do you have an aftermarket BOV or aftermarket intake?
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    By gear box to you mean the section of the transmission? Aftermarket intake, no. BOV, yes. It is not the 5 speed that came on the car. It is a 6 speed.
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    Quote Originally Posted by itWRXjustfine View Post
    By gear box to you mean the section of the transmission? Aftermarket intake, no. BOV, yes. It is not the 5 speed that came on the car. It is a 6 speed.
    Gearbox = transmission.

    Is the harness connected well?
    Does the idle improve when you fit the correct BPV instead of the aftermarket BOV?
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    Not sure. I bought the car with the BOV installed. I take it you are implying that my BOV is leaking. I read the BOV article on NASIOC and I think that I will get to adjusting mine according to that. As far as the gearbox goes, there is a unconnected wire, I inquired about it in a previous post but no response. I was wondering if when switching to a 6speed on a WRX if you are supposed to have any wires that don't plug into anything.
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    Registered User Sarra's Avatar
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    Quote Originally Posted by itWRXjustfine View Post
    Not sure. I bought the car with the BOV installed. I take it you are implying that my BOV is leaking. I read the BOV article on NASIOC and I think that I will get to adjusting mine according to that. As far as the gearbox goes, there is a unconnected wire, I inquired about it in a previous post but no response. I was wondering if when switching to a 6speed on a WRX if you are supposed to have any wires that don't plug into anything.
    Do you have a DCCD controller? Or, is there a DCCD switch, and an STi cluster in the car? It MIGHT be the DCCD wiring, if it's a USDM or DCCD equipped JDM 6MT.

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    Moderator Donkey's Avatar
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    The NPS should be on the side of the tranny along with the back up light switch. Do you not have back up light either?
    The NPS uses the brown connector from the harness and the backup switch uses the grey. The NPS itself should show 1 ohm or less in neutral between the 1 and 3 pins. In gear should be 1 megaohm or more between the 1 and 3 pin.


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    What year 6 speed do you have? Also from reading sometimes you have to use the same sensor the ECU uses. So You would need a 5speed sensor from a 04/05 WRX.
    Last edited by Donkey; 12-02-2009 at 09:39 AM.
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    No I dont have DCCD at all. Sorry in the spur of things I accidentally started another thread about this issue with some pics.

    Supremely Confused with my 6speed
    Last edited by itWRXjustfine; 12-04-2009 at 06:13 PM.
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