# 1995 Nissan truck rough idle



## zootal (Sep 27, 2007)

1995 Nissan truck. 2dr 4 cyl MT a/c. 180,000 miles or so.

The engine idles rough, and the idle speed is a bit erratic, speeds up a bit, slows down a bit and sometimes stalls. Off idle and faster, it is as smooth as can be. Step on the gas a bit and it takes off as smooth as can be. Power is good, mileage is good. It drives just fine. But I step on the clutch, take my foot off of the gas, and it idles slow and rough with occasional stalling. This is not new - it's done it for maybe six months, and it is very slowly but surely getting worse. I checked the ECU, and there are no fault codes. Whatever is causing this, it's not bad enough for the ECU to detect a problem.

I checked for vacuum leaks and found nothing - no sign of a leak. Plugs are clean. I even pulled the distributor cap, and it is shiny clean inside. I trickled a few drops of carb cleaner down the intake, and I did not get the increase in engine speed you would expect if there were a vacuum leak causing a lean mixture. I checked the MAF sensor and got between .5 increasing to 1v or so at the output when revving the engine, which I think is normal.

What gets me is that off-idle and faster, it is as smooth as can be. It only stumbles at idle. That eliminates a whole slew of potential problems, but leaves me not sure where to even look. I'm thinking of replacing the EGR valve thinking it might be leaking, and eyeballing the O2 sensor, but I hesitate to just start throwing money at this.

Anyone have any experience with this sort of thing on this model?


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## jp2code (Jun 2, 2011)

Experience with it? No, but I can give information.

First, I would suggest making sure your ignition timing is correctly set to 14° using a Timing Light. A lot of problems can show up if the timing gets off.

Next, I'd say to pull the error codes off the ECU to see if it is reporting anything. I did a write-up on another forum where I included a video and the list of error codes.






[VIDEO] Checking Error Codes - Infamous Nissan - Hardbody / Frontier Forums


[VIDEO] Checking Error Codes Hardbody Forum (D21)



www.infamousnissan.com





In the 1995 Service Manual, page EF&EC-42 shows that the MAF should read between 1 and 3 volts while the engine is running. You can unplug the MAF to see if the idle speed improves. If it does, the MAF is either dirty, has a bad connection or a bad engine ground. If you leave it unplugged, your truck will drive horrible around 2500 RPM because the ECU will be in limp mode.










My guess, though, would be the Idle Air Control Valve, IACV, or Swirl Control Valve, SCV, is malfunctioning. They usually start messing up when the passages get clogged with carbon, making the device not function correctly. You could clean them out or replace them.

It could also be a bad temperature sensor. That would not give a Check Engine Light, but it should show up by reading the codes. If the truck always thinks the engine is cold, the ECU would have a hard time trying to regulate the idle speed.

If none of those is the issue, I'd go back to the vacuum leak issue. If your Clutch Fan works, you can find vacuum leaks easily. 

Get a clamp or a pair of vice grips and clamp that to the radiator fan shroud to prevent the fan from turning while the engine is running.
Crank the engine. You will not have any airflow because the clamp is holding the radiator fan stationary.
Make short burst squirts of Starter Fluid around the engine in different spots, allowing the Starter Fluid to dry before moving to the next spot. After you squirt Starter Fluid on some vacuum lines, reach down with your hand and move those vacuum hoses around a bit. Sometimes a cracked line needs to be flexed in order for the hole to open up. Starter Fluid is VERY volatile. It is more combustible than gasoline, so be extremely careful. If you squirt somewhere that there is a spark, like a bad spark plug cable, you could have a fire in the engine bay. That's one reason to only make short squirts.
If you squirt in any area that increases engine idle speed, try to narrow down that area by squirting on individual hoses and components until you have found the leak. Leaks can also be found on the Intake Manifold, so be sure to squirt a little around there too.
Do not let the engine run for long. I'd say 3 to 5 minutes tops. If the radiator hose starts to get warm, turn the engine off.
Remember to take the clamp or Vice Grips off of the Radiator Shroud afterward!
Good luck


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## rogoman (Dec 16, 2004)

zootal said:


> 1995 Nissan truck. 2dr 4 cyl MT a/c. 180,000 miles or so.
> 
> The engine idles rough, and the idle speed is a bit erratic, speeds up a bit, slows down a bit and sometimes stalls. Off idle and faster, it is as smooth as can be. Step on the gas a bit and it takes off as smooth as can be. Power is good, mileage is good. It drives just fine. But I step on the clutch, take my foot off of the gas, and it idles slow and rough with occasional stalling. This is not new - it's done it for maybe six months, and it is very slowly but surely getting worse. I checked the ECU, and there are no fault codes. Whatever is causing this, it's not bad enough for the ECU to detect a problem.
> 
> ...


Check out this web site for a *FIX* that someone did who had a similar problem such as yours:






FIX: erratic idle, low speed driveability, possibly more - Infamous Nissan - Hardbody / Frontier Forums


FIX: erratic idle, low speed driveability, possibly more Wiring and Electrical



www.infamousnissan.com





The proper and most accurate way to check the intake system for a vacuum leak, is to attach a vacuum gauge to a *full* vacuum source. With the engine fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be around 21 InHg. If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. The gasket may have failed; *spray a water mist* at the gasket to see if the gauge reading changes. Also check the intake plenum bellows at the throttle valve and at the MAF for cracks or loose clamps.


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## zootal (Sep 27, 2007)

1) Can timing even be set on this model? I've never touched it, and I've owned the truck for 24 years. I do have a timing light - I was a mechanic in another life, back when we had to adjust point gap and set timing manually (we didn't need no stinkin' computers  ), but that was the 1970s and things are a bit different today....
2) I need to check MAF voltage again - it was NOT that high, it barely cleared one volt when revving the engine. And the input voltage was only 10v, not battery voltage. Amazon has these for under $35, but are those generally reliable?
3) No error codes from the ECU, that was the first thing I checked.
4) Is the factory manual downloadable or otherwise available anymore?

TYVM for the info, gives me things to do. I'll check these and report back.


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## rogoman (Dec 16, 2004)

Yes, I remember those days going back to the 50's. Life was so simple back then; didn't even need a timing light; just listen to the engine when setting the distributor. Today we have to be electronic technicians as much as regular mechanics. It's a new world out there.

The ignition timing can be set on your engine because it has a distributor. Late model engines don't have a distributor; each spark plug has it's own ignition coil that's pulsed from the ECU, so you have no control of the timing.

The black wire on the MAF harness should be pin 1. The green/red wire should be pin 3; the 12v supply.
Here's a picture of the MAF diagnostic test taken from the FSM:










You can download an FSM from this website:






Nissan Hardbody D21 Truck Service Repair Manuals


Nissan Hardbody D21 Truck Service Repair Manual PDF Free Download 1989 1990 1994 1995 1996 1997




diyservicemanuals.com


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## smj999smj (Jan 1, 2006)

Sounds like it's lean. Common areas would be a leak at the intake gasket or throttle body gasket. Get a damp rag and place it over the throttle body opening and see if you can keep the engine running with the throttle; if you can, then it is sucking air from some place. Sticking EGR valves were more common on 96 models, but I wouldn't rule it out. There were also some issues with grounds to several sensors caused by poor connections at splice crimps in the EGI harness. There were several of them in the engine harness where it runs alongside the valve cover. One would have to remove the harness protector and cut off of the electric tape around some of the crimp splice connections. Then the splice joint would be soldered and everything put back together, again. As far as any kind of engine management parts or sensors, it's best to stick with genuine Nissan or OE parts, such as Hitachi, NTK and Denso. You could unplug the front O2 sensor and see what happens; the ECM will go into O2 fail safe mode and use a 0.33v reference voltage to run the engine. If it runs better, it may have a faulty upstream O2 sensor. Again, stick with an OE part, which would be NTK or Denso; Rockauto usually sells both. Ignition timing usually never falls out of spec unless the distributor is moved, but just make sure you check it in ECM timing set mode per the manufacturer procedure. Engine will be warmed up and TPS will be unplugged during the adjustment.


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## zootal (Sep 27, 2007)

So the adventure continues. I replaced the MAF. Now it runs about 80% better. It no longer stalls, but the idle will intermittently fluctuate. It is not consistent. It will idle normally for a while, and then start to fluctuate. Run normal for a while longer, then start to fluctuate. It's irregular, but will do it every 5-15 seconds. With the new MAF it still does this, just not as bad, as with the old MAF it will stall. I took it our for a drive, and it runs great. Plenty of power, nice and smooth once you get it off idle. 

AND the CEL comes on, the ecu is flashing bad MAF code. I check the two wires that run from maf to ecu for ground and continuity. They check OK. I check the power into the MAF. It is OK. I see nothing wrong with the wiring, ground or power.

I've checked for vacuum leaks extensively, even replaced a few questionable vacuum hoses. I'm about 99.9% sure there are no vacuum leaks.

And now I'm wondering if my made in China MAF is not all that good, or the ecu itself might have a problem in the maf sensor circuit (it is 25 years old, after all), or if I'm just missing something?


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## zootal (Sep 27, 2007)

so wtr the O2 sensor, would a bad O2 sensor cause something like this? Because it runs great off-idle up to 5000rpm, it just won't idle smooth and consistent. I thought of slapping in a new O2 sensor.

Edit: So I unplgged the front O2 sensor. No difference. I notice it cuts out up to about 1500 RPM. It's, worse at idle, noticeble at say 1200, and from there up I don't really notice it at all. Good power. It will scream down the freeway with no problem.


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## zootal (Sep 27, 2007)

Aaaanndd to make it more interesting, I've found a couple of conversations where other people had the _exact_ same problem. They were unable to fix it. I'm going to take a look at the iac valve, I did find one report of replacing it fixing this problem. But that doesn't explain why it idles smooth with the maf unplugged. Or why a new MAF makes it partially better unless the new made in china maf is no good to start with. And IIRC the iac only works at idle, and should not effect the off-idle - or should it?


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## jp2code (Jun 2, 2011)

If you unplug the MAF and the idle gets better, there is an issue with it somewhere. 

If the MAF is OK, check the ignition timing. It should be around 10 degrees. 

If those are fine, try unplugging one spark plug wire. If the idle gets worse, that wire is ok. Plug it back in and try the next one.


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## rogoman (Dec 16, 2004)

zootal said:


> so wtr the O2 sensor, would a bad O2 sensor cause something like this? Because it runs great off-idle up to 5000rpm, it just won't idle smooth and consistent. I thought of slapping in a new O2 sensor.
> 
> Edit: So I unplgged the front O2 sensor. No difference. I notice it cuts out up to about 1500 RPM. It's, worse at idle, noticeble at say 1200, and from there up I don't really notice it at all. Good power. It will scream down the freeway with no problem.


You may have one or more dirty fuel injectors that could cause rough idling and run good at highway speeds. Run some good injection cleaner, like BG products 44K, through the system; give the cleaner about a week or two to do it's job. With the 180,000 mi that you have on your truck, it might be a good idea to get the injectors cleaned up with a chemical flush or just replace all the injectors with re-man'd injectors.


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## zootal (Sep 27, 2007)

jp2code said:


> If you unplug the MAF and the idle gets better, there is an issue with it somewhere.
> 
> If the MAF is OK, check the ignition timing. It should be around 10 degrees.
> 
> If those are fine, try unplugging one spark plug wire. If the idle gets worse, that wire is ok. Plug it back in and try the next one.


I miss the days when I would hook up a scope and exhaust analyzer, spend a few minutes and know the problem. I did that for a living. I overhauled several carbs a week, and had 100% success rate with them. Sadly, those days are gone....

Unplugging the MAF makes the idle problem go away, but the old and new MAF did the same thing. I'm not sure if that is the cause, or just a symptom of something else wrong. I did check the wires to the maf, power and the two wires that go into the ecu under that passenger seat. They are fine.

The suggestion to clean/replace the injectors has merit. It was suggested I stick to certain brands for the MAF, and I'm not 100% certain the cheap made in China MAF I have is working 100%, so getting a brand name MAF also has merit. I'm not sure about the IAF, as that could cause the problem. And now I'm looking at spending more money than the truck is worth <sigh>. I went down this rabbit hole with my old Subaru. $1000 later I threw in the towel, flushed a thousand bucks and retired the car. I see this happening again with this truck...


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## jp2code (Jun 2, 2011)

When you unplug the MAF, the ECU uses programmed data to idle the engine using default data. It just doesn't have data to run at highway speeds.

You could try getting some MAF Cleaner. Most auto parts stores carry it. 

Personally, I try to spray my MAF wire down with MAF cleaner while I am replacing the air filter.

I bought this little dual pack of MAF cleaner and throttle body cleaner in 2015, and the can still has plenty in it.



https://www.amazon.com/gp/product/B0091KCH6U


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## BRubble (Jun 22, 2014)

rogoman said:


> Check out this web site for a *FIX* that someone did who had a similar problem such as yours:
> 
> 
> 
> ...


Zootal,

I had a '93 4cyl AT KC Hardbody for 20 year's and every blue moon mine would have an overnight cold engine idle problem. It would only start if I gave it some gas, and only continue to idle if I gave it some gas. After maybe 30 second's or so, it would idle on it's own, without me giveing it gas. It only did this maybe once a year or so, and it would clear up, so it wouldn't have done me any good to take it to Nissan, cause by the time I got there the engine would be running and idleing fine.

Check out the Link that RogoMan provided and go through that procedure to see if getting those connection's reconnected and soldered will give you any relief. The symptom's described does seem to be closely related to the problem that I was haveing with the '93 that I had. I don't have the '93 anymore. After 20 year's I just wanted a New Truck with more power for pulling my utility trailer.

I hope it is something as simple as this and will get your truck straightened out.

Regards,


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## jp2code (Jun 2, 2011)

BRubble said:


> Zootal,
> 
> I had a '93 4cyl AT KC Hardbody for 20 year's and every blue moon mine would have an overnight cold engine idle problem. It would only start if I gave it some gas, and only continue to idle if I gave it some gas. After maybe 30 second's or so, it would idle on it's own, without me giveing it gas. It only did this maybe once a year or so, and it would clear up, so it wouldn't have done me any good to take it to Nissan, cause by the time I got there the engine would be running and idleing fine.
> 
> ...


Is this Tony from Infamous????


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## BRubble (Jun 22, 2014)

jp2code said:


> Is this Tony from Infamous????


Hey JP2,

No not me, sorry. Just an average Barney that had a '93 4cyl Hardbody for 20 year's. It was a good Truck.

Regards,


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## zootal (Sep 27, 2007)

I just realized something. Since it idles fine with the MAF unplugged, that would eliminate the injectors as the cause of the problem. And the timing. And vacuum leaks. And the IAF valve. And a whole slew of things that could cause the problem..... sadly it doesn't give me a clue where to look next, but now I'm suspecting that brand new made in China MAF might be the culprit....


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## jp2code (Jun 2, 2011)

Exactly. The problem is somewhere with the MAF. It could be bad wires going to it, corroded contacts, or a dirty MAF wire.

Since you recently replaced the MAF, it likely isn't a dirty MAF wire, so I'd look for bad wires around the connector.

Here is a link to the EC section of the 1995 Service Manual:









EC.pdf | Powered by Box







app.box.com





There is a section on how it is wired up on (EC-18 for the V6) or (EC-63 for the 4-cylinder). 

On EC-103, it shows Terminal 16 expects 1-3 Volts with the engine running.


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## zootal (Sep 27, 2007)

jp2code said:


> Exactly. The problem is somewhere with the MAF. It could be bad wires going to it, corroded contacts, or a dirty MAF wire.
> 
> Since you recently replaced the MAF, it likely isn't a dirty MAF wire, so I'd look for bad wires around the connector.
> 
> ...


I checked the wires. Terminals are clean. No grounds. Good continuity to computer under passenger seat, I disconnected the conntecter from it and checked. Power into MAF is good. I think I'm going to try to find another MAF, and this time get a name brand unit, not some el-cheapo made in China MAF.


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## zootal (Sep 27, 2007)

smj999smj said:


> <snip> it's best to stick with genuine Nissan or OE parts, such as Hitachi, NTK and Denso. ...


I found one by Delphi. Any comments on the quality of that brand? I also see Cardone and Blue Streak, but I'm not familiar with those brands.


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## jp2code (Jun 2, 2011)

1995 NISSAN PICKUP 3.0L V6 Mass Air Flow (MAF) Sensor | RockAuto


RockAuto ships auto parts and body parts from over 300 manufacturers to customers' doors worldwide, all at warehouse prices. Easy to use parts catalog.



www.rockauto.com





Hitachi is OEM, but DELPHI and Cardone should also be good.


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## zootal (Sep 27, 2007)

And why do so many of the ones being sold look like the Hitachi part, but with the names "Nissan" and "Hitachi" scratched off of the case? Do they take used ones, remove the name, clean it and resell it?


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## jp2code (Jun 2, 2011)

Probably from the same mold. These have been built for 30+ years


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## zootal (Sep 27, 2007)

So many hours later and much $$, I think it is time to retire this truck. I've traced wiring all over, checked grounds, replaced the maf twice. At this point everything points to the control unit under the seat as being bad, but I've been down that rabbit hole with a different car and I'm not doing it again. I have found reports of others with the exact same symptoms, and they were not able to fix it either. Thanks everyone for you help.


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## jp2code (Jun 2, 2011)

You should update your original thread so that others can follow what this is about.


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## zootal (Sep 27, 2007)

Huh, apologies, forgot there were two threads, not sure why I did that. This has been done.


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