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ChrisFreeman

Quick Question-Where is the idle adjustment screw

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I can not find the Idle adjustment screw and I was wondering if anybody can tell me where it is. Thanks in advance.

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I think all of that is controlled by the ECU, isn't it? I think there is an idle troubleshooting flowchart in the FSM, available in the Garage section......

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Mine has a little line on the top of the engine that I moved one ball. My idle was very low and shook the car now its smooth.

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The idle adjustment screw for the vg30e is on the driver side of the intake manifold. It will be on the underside of the manifold right next to the firewall with the head facing the brake booster.
The screw is about the size of a dime and is sometimes covered with sealant or a rubber plug (not needed).

Make 1/4 and half turn adjustments revving the engine lightly and letting it settle OUT it faster (counter clockwise).

Factory idle with everything off and IACV plugged in is 750 +/- 50 RPM

You may find 800-850 is a little smoother, no need to go over 900.

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The idle adjustment screw for the vg30e is on the driver side of the intake manifold. It will be on the underside of the manifold right next to the firewall with the head facing the brake booster.

The screw is about the size of a dime and is sometimes covered with sealant or a rubber plug (not needed).

Make 1/4 and half turn adjustments revving the engine lightly and letting it settle OUT it faster (counter clockwise).

Factory idle with everything off and IACV plugged in is 750 +/- 50 RPM

You may find 800-850 is a little smoother, no need to go over 900.

 

Okay thanks I found it! But there is a problem I have turned the screw, and revved the engine around 2000 rpm and then let it settle and I have done this quite a few times but with no change. What could be the problem?

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What's it idling at? I think the screw stops turning up idle when you are about 1 thread from flush.
-Do you have an EGR leak? This can bring your idle down.

-Is the wire harness from your valve cover to your IACV intact? (plugs into the opposite side of where your idle screw is, hard to see)

-How are your spark plugs?

 

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On mine that screw makes no difference and when you unplug the iacv sub harness like the fsm says to, the rpms drop to like 250. Sorry to thread jack but we might have the same issue lol.

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Adjusting idle VIA the IACV screw is not the proper approach, that's why its covered in epoxy, its set at the factory.

 

If the truck is running properly the ecu will adjust the idle itself. Did you adjust the idle VIA the ecu idle adjustment first? Check for vacuum leaks and corroded/broken wiring. Your IACV/idle solenoid may have dirty connections or may be plugged with carbon. A good cleaning is all they usually need in my experience.

 

240sx and 300zx do the exact same thing.

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Adjusting idle VIA the IACV screw is not the proper approach, that's why its covered in epoxy, its set at the factory.

 

If the truck is running properly the ecu will adjust the idle itself. Did you adjust the idle VIA the ecu idle adjustment first? Check for vacuum leaks and corroded/broken wiring. Your IACV/idle solenoid may have dirty connections or may be plugged with carbon. A good cleaning is all they usually need in my experience.

 

240sx and 300zx do the exact same thing.

 

This is wrong information. You cannot adjust the Idle Via the ECU with the pathfinder The proper procedure is as follows.

 

FSM 1994 Pathfinder EF/EC Page 26

Disconnect IACV-AAC valve sub-harness connector.

Adjust engine speed by turning idle speed adjusting screw (A/T in "N" position).

A/T: 700 rpm

M/T: 700 rpm

 

(Then there's an Arrow pointing to an Illustration of the idle screw under intake)

 

Reconnect IACV-AAC valve sub-harness connector.

 

While specified in the FSM unplugging this is not really necessary unless you suspect it is being problematic. So Like I said earlier...

Factory idle with everything off and IACV plugged in is 750 +/- 50 RPM

You may find 800-850 is a little smoother, no need to go over 900.

And if it won't go up to at least 750 plugged (or 700 unplugged) something else may be wrong.

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Adjusting idle VIA the IACV screw is not the proper approach, that's why its covered in epoxy, its set at the factory.

 

If the truck is running properly the ecu will adjust the idle itself. Did you adjust the idle VIA the ecu idle adjustment first? Check for vacuum leaks and corroded/broken wiring. Your IACV/idle solenoid may have dirty connections or may be plugged with carbon. A good cleaning is all they usually need in my experience.

 

240sx and 300zx do the exact same thing.

 

This is wrong information. You cannot adjust the Idle Via the ECU with the pathfinder. YES I am aware some have sticker on the ECU that says "Idle Adjustment" this sticker is wrong from the factory, the correct sticker displays a warning about not over turning the diagnostics screw.

 

NOW The proper procedure is as follows.

 

FSM 1994 Pathfinder EF/EC Page 26

Disconnect IACV-AAC valve sub-harness connector.

Adjust engine speed by turning idle speed adjusting screw (A/T in "N" position).

A/T: 700 rpm

M/T: 700 rpm

 

(Then there's an Arrow pointing to an Illustration of the idle screw under intake)

 

Reconnect IACV-AAC valve sub-harness connector.

 

While specified in the FSM unplugging this is not really necessary unless you suspect it is being problematic. So Like I said earlier...

Factory idle with everything off and IACV plugged in is 750 +/- 50 RPM

You may find 800-850 is a little smoother, no need to go over 900.

It also begins with page 25 about checking the ignition timing first AND loops back to page 25 to verify the timing after the idle has been set. If your timing is too retarded your idle will drop if your timing is advanced your idle will come up some. Proper setting 15 BTDC +/- 2.

And if it won't go up to at least 750 plugged (or 700 unplugged) something else may be wrong.

Edited by MY1PATH

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This is wrong information. You cannot adjust the Idle Via the ECU with the pathfinder. YES I am aware some have sticker on the ECU that says "Idle Adjustment" this sticker is wrong from the factory, the correct sticker displays a warning about not over turning the diagnostics screw.

 

NOW The proper procedure is as follows.

 

FSM 1994 Pathfinder EF/EC Page 26

Disconnect IACV-AAC valve sub-harness connector.

Adjust engine speed by turning idle speed adjusting screw (A/T in "N" position).

A/T: 700 rpm

M/T: 700 rpm

 

(Then there's an Arrow pointing to an Illustration of the idle screw under intake)

 

Reconnect IACV-AAC valve sub-harness connector.

 

While specified in the FSM unplugging this is not really necessary unless you suspect it is being problematic. So Like I said earlier...

Factory idle with everything off and IACV plugged in is 750 +/- 50 RPM

You may find 800-850 is a little smoother, no need to go over 900.

It also begins with page 25 about checking the ignition timing first AND loops back to page 25 to verify the timing after the idle has been set. If your timing is too retarded your idle will drop if your timing is advanced your idle will come up some. Proper setting 15 BTDC +/- 2.

And if it won't go up to at least 750 plugged (or 700 unplugged) something else may be wrong.

 

 

Sorry it took so long to respond. I got tired of messing with the truck and when I went to start it up, everything was great. The truck was running nice and smooth. If this problem comes back, would this indicate a clogged IACV?

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Things to check for:

Ignition timing too retarded

Worn spark plugs/ misfire

Leaking EGR valve
Accessory load (binding pulleys, alty etc)

Corroded IACV harness or bad wire/ connector
Clogged IACV, or otherwise sticking... there is a little magnetic piston that slides back and forth inside there. If it gets corroded it can stick.

 

Altitude... both my trucks idle about 100 rpm higher at sea level and its only 2,500FT here.

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If your truck is running properly you don't need to adjust that screw!!! The ecu does set the idle. Its listed right in the factory specs in tunercode! You set target rpm and the ecu will adjust to whatever u set it to in the tune. its set to 700 +/- 50 from the factory. Changing this value in your bin file will change your rpm internally in yhe ecu. The ecu does set the idle. Adjusting iacv is a method i wouldnt do.

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The only reason your idle is not in thst range is because u have something else wrong. I personally wouldnt mask a problem by just manually adjusting idle. Fix the problem that is making your idle fall out of spec and the ecu will do the rest.

 

If you are trying to set an idle other than factory than go for it although its totally uneccessary. Proper way to change idle is to change the Target rpm value in the tune itself.

Edited by Nefarious

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The only reason your idle is not in thst range is because u have something else wrong. I personally wouldnt mask a problem by just manually adjusting idle. Fix the problem that is making your idle fall out of spec and the ecu will do the rest.

 

If you are trying to set an idle other than factory than go for it although its totally uneccessary. Proper way to change idle is to change the Target rpm value in the tune itself.

 

Ok Chris, good luck doing something totally unnecessary.

I'm gonna take my smooth running pathy with a higher than stock idle somewhere else.

Edited by MY1PATH

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The argument interested me enough to push me into the rabbit hole, so here we go.

If the truck is running properly the ecu will adjust the idle itself. Did you adjust the idle VIA the ecu idle adjustment first? Check for vacuum leaks and corroded/broken wiring. Your IACV/idle solenoid may have dirty connections or may be plugged with carbon. A good cleaning is all they usually need in my experience.


This is wrong information. You cannot adjust the Idle Via the ECU with the pathfinder. YES I am aware some have sticker on the ECU that says "Idle Adjustment" this sticker is wrong from the factory, the correct sticker displays a warning about not over turning the diagnostics screw.


Near as I can tell, Nefarious is talking about adjusting the idle speed by reprogramming the ECU, not screwing with the mislabeled diagnostic pot. It's an odd point to bring up (seeing as how most of us don't have the tools to reflash our ECUs) but he is correct in that setting the idle from the ECU should not be necessary. If the engine's idling too high or too low, it's not that the computer has the wrong goal, it's that, for whatever reason, the idle air valves can't make it happen.

 

I had a look at the EF&EC section (page 14 specifically) to get a better idea of what goes on in the idle air assembly. The computer controls the engine's idle via the Auxiliary Air Control valve, which appears to be a simple solenoid valve that varies airflow by duty cycle (not unlike a fuel injector). This part allows the computer to adjust the idle. (High idle during warmup is handled by the IACV, which as far as I can tell does not communicate with the computer.) Small adjustments to the screw don't change the idle because the computer tunes them out with the AAC. With large adjustment or mechanical issues (or the IACV being open) the idle can and does change, so clearly the AAC can only do so much.

 

I suspect that the purpose of the idle adjustment screw is to get the idle close enough to right that the AAC can fine-tune it. This would explain why the FSM's adjustment procedure for the screw says to disconnect the idle air assembly first.

 

True, adjustments to this shouldn't be necessary on a stock vehicle, but after years of ingesting PCV gunk and whatever else I'll bet the air flow through the throttle body changes somewhat. Thorough cleaning/repair of the throttle body and the idle air valves would probably be the proper fix, but I don't imagine that simply adjusting the system to work around the gunk/leaks/etc would blow your engine, fry your ECU, or retroactively lose WWII for the Allies.

 

If you've done significant intake/engine mods you may want to adjust it anyway. :shrug:

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The argument interested me enough to push me into the rabbit hole, so here we go.

 

 

Near as I can tell, Nefarious is talking about adjusting the idle speed by reprogramming the ECU, not screwing with the mislabeled diagnostic pot. It's an odd point to bring up (seeing as how most of us don't have the tools to reflash our ECUs) but he is correct in that setting the idle from the ECU should not be necessary. If the engine's idling too high or too low, it's not that the computer has the wrong goal, it's that, for whatever reason, the idle air valves can't make it happen.

 

I had a look at the EF&EC section (page 14 specifically) to get a better idea of what goes on in the idle air assembly. The computer controls the engine's idle via the Auxiliary Air Control valve, which appears to be a simple solenoid valve that varies airflow by duty cycle (not unlike a fuel injector). This part allows the computer to adjust the idle. (High idle during warmup is handled by the IACV, which as far as I can tell does not communicate with the computer.) Small adjustments to the screw don't change the idle because the computer tunes them out with the AAC. With large adjustment or mechanical issues (or the IACV being open) the idle can and does change, so clearly the AAC can only do so much.

 

I suspect that the purpose of the idle adjustment screw is to get the idle close enough to right that the AAC can fine-tune it. This would explain why the FSM's adjustment procedure for the screw says to disconnect the idle air assembly first.

 

True, adjustments to this shouldn't be necessary on a stock vehicle, but after years of ingesting PCV gunk and whatever else I'll bet the air flow through the throttle body changes somewhat. Thorough cleaning/repair of the throttle body and the idle air valves would probably be the proper fix, but I don't imagine that simply adjusting the system to work around the gunk/leaks/etc would blow your engine, fry your ECU, or retroactively lose WWII for the Allies.

 

If you've done significant intake/engine mods you may want to adjust it anyway. :shrug:

 

I like this explanation. I was wondering this myself. Why does the pot on the ECU say idle speed adjustment? Does it actually adjust the idle speed? If not, what does it do?

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I've never properly tested it to see if there's any correlation between its position and idle speed... but I know that each time I've checked for codes I've lost track of its original position, and my idle hasn't changed noticeably.

 

IMO either they wanted to keep us out of it or it was originally intended it to function as some kind of adjuster. The second would make more sense to me... triggering diagnostic modes with a pot seems like a needlessly complex way of doing it as opposed to, I don't know, a couple of buttons, unless they'd already designed around a pot.

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I've never properly tested it to see if there's any correlation between its position and idle speed... but I know that each time I've checked for codes I've lost track of its original position, and my idle hasn't changed noticeably.

 

IMO either they wanted to keep us out of it or it was originally intended it to function as some kind of adjuster. The second would make more sense to me... triggering diagnostic modes with a pot seems like a needlessly complex way of doing it as opposed to, I don't know, a couple of buttons, unless they'd already designed around a pot.

 

Let me put ti nice and simply, I'm no mechanic, but I happen to have pretty much the same problem, (my truck constantly looses its idle, it soars up to 12RPM and runs really rough) from reading all comments up to yours I do have a question, when you recommended to clean the tubing inside the plenum where carbon deposits should be normal, after all we're talking about a 20 plus years vehicle would you also recommend checking the EGR for the same purpose as well as the AACV, mine was replaced four years ago and the EGR was also replaced more recently, the old one was practically blocked with soot and dirt, truly hope you"re still around your comments are right to the point and the make a lot of sense....

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I haven't torn into an idle air system because mine hasn't gone south on me yet, but I don't remember finding anything in the lines that go to it. The idle air system taps into the rubber intake pipe at about the same point as the PCV system (where the gunk comes from), so I imagine most of the throttle body gunk is sucked into the motor before it can make its way into the idle air system. Between that and how you just replaced the valve, unless the idle issue started when you replaced it, I would leave that system alone for the time being.

I don't think EGR would cause high idle (assuming you mean 1200 rpm not 12). IIRC it should be closed at idle, and should lower the idle or choke the engine out entirely if you open it manually. My first thought is, how old are your vacuum lines? If you have a vacuum leak, either from the lines or from the rubber part of the intake, the engine will idle higher, and likely rougher as the mixture gets skewed lean. Vacuum hose is cheap. There should be a routing diagram under the hood in case you forget what went where, but if you replace one line at a time it's hard to screw it up. Cleaning out the throttle body while you're in there wouldn't hurt (and actually gave my '95 some power back) but unless there's a glob of something preventing it from closing fully, I doubt the TB is what's making it idle high.

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About a month ago I got my valve cover gaskets and rear main seal redone on my 93 WD21, and shortly after getting it back I noticed that my oil light would come on when I would stop and idle after a few minutes of driving around then turn off when I accelerate. It has been running totally fine with no noticeable loss of power, roughness or anything like that and I just went on a 3 hour road trip last weekend where it ran great the whole time even when off-roading,doing doughnuts and stunt driving. In other words it still seems to run as great as always, but it still has me concerned to a small degree as it wasn't doing that before. I already had the sending unit replaced with a genuine Nissan part and had an oil pressure test performed by Nalley Nissan and they said the oil pressure was on the low end, but was still within range where they weren't really sure if it should come on at all. They also changed the oil to the most heavy duty oil available, but it was still coming on. I turned the idle control a couple of clicks counterclockwise and idled it up to around 850-900 RPM's +-. it looks like it pretty much stopped the light from coming on for the better part as long as the A/C is off. If I turn the A/C on, the oil light comes on and stays on until I turn off the A/C. Additionally, the strangest part is that before I adjusted the idle control, when I was sitting at idle and the light would flicker on and off, if I turned on my headlights, it would stay on longer and brighter. Has anyone ever experienced this before? Is it possible that the light coming on has something to do with the electrical system more so than low pressure? Nalley Nissan did extensive diagnostics and really didn't sound any alarms, but I still want to troubleshoot the problem.

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About a month ago I got my valve cover gaskets and rear main seal redone on my 93 WD21, and shortly after getting it back I noticed that my oil light would come on when I would stop and idle after a few minutes of driving around then turn off when I accelerate. It has been running totally fine with no noticeable loss of power, roughness or anything like that and I just went on a 3 hour road trip last weekend where it ran great the whole time even when off-roading,doing doughnuts and stunt driving. In other words it still seems to run as great as always, but it still has me concerned to a small degree as it wasn't doing that before. I already had the sending unit replaced with a genuine Nissan part and had an oil pressure test performed by Nalley Nissan and they said the oil pressure was on the low end, but was still within range where they weren't really sure if it should come on at all. They also changed the oil to the most heavy duty oil available, but it was still coming on. I turned the idle control a couple of clicks counterclockwise and idled it up to around 850-900 RPM's +-. it looks like it pretty much stopped the light from coming on for the better part as long as the A/C is off. If I turn the A/C on, the oil light comes on and stays on until I turn off the A/C. Additionally, the strangest part is that before I adjusted the idle control, when I was sitting at idle and the light would flicker on and off, if I turned on my headlights, it would stay on longer and brighter. Has anyone ever experienced this before? Is it possible that the light coming on has something to do with the electrical system more so than low pressure? Nalley Nissan did extensive diagnostics and really didn't sound any alarms, but I still want to troubleshoot the problem.

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Check the wire to the sending unit. It is to the left of the oil filter, hard to reach but it is common for people to mess up the wire during an oil change. It could be grounding out on something.

 

I would also have the oil pressure checked to be sure as well.

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