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I have a 1993 Nissan d21 4cyinder. Cold start it isles fine…

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I have a 1993 Nissan...
I have a 1993 Nissan d21 4cyinder. Cold start it isles fine drives fine. Once fully warmed up it still drives find but the idle is a bit rough and while cruising you can hear the exhaust not purring smoothly it has a slight popping sound like a misfire. On a hot restart it will start but the idle will drop below 500 rpm unless you rev it up a couple times then it will idle at 750 and stay there sill idling slightly rough. When you turn the ac on it will idle up. It also smells like it’s running rich when it starts to act up when warm. Have already replaced coolant temp sensor, checked ignition timing, replaced spark plugs, wires and dust cap. Please help
Submitted: 2 months ago.Category: Nissan
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Answered in 5 minutes by:
12/21/2017
Nissan Mechanic: Jay, Nissan Technician replied 2 months ago
Jay
Jay, Nissan Technician
Category: Nissan
Satisfied Customers: 21,119
Experience: 20+yrs experience with Nissan & Infiniti Trained & Certified.Currently still working for Dealer
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Hello my name is ***** ***** thank you for your question.

What brand spark plugs did you install?

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Customer reply replied 2 months ago
Ngk. Same problem was there before I changed the spark plugs
Nissan Mechanic: Jay, Nissan Technician replied 2 months ago

The only thing I can say I would check for this then is the distributor. The distributor has a signal plate type cam sensor, if the signal plate shifts, it can cause your issue.

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Nissan Mechanic: Jay, Nissan Technician replied 2 months ago

or a lazy optical sensor that reads off that signal plate. But this is most commonly caused by the distributor, but I would have it checked to verify.

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Customer reply replied 2 months ago
Why the difference when cold Vs warm?
Nissan Mechanic: Jay, Nissan Technician replied 2 months ago

Temperature. Electronics as it builds heat is when it could act up.

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Customer reply replied 2 months ago
It’s like clockwork, once the car is out of cold start high idle mode is when it starts. Any other possibilities?
Nissan Mechanic: Jay, Nissan Technician replied 2 months ago

That is the most common, but if it's a low engine idle when in gear you are feeling this engine running ruff, say around 500 rpms ( that is to low ) then it could be a Idle Air Control valve. That is what controls base idle.

Is it only ruff at idle or do you also feel it when driving?

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Customer reply replied 2 months ago
Has normal power but you can hear it slightly sputtering while cruising. Truck is 5speed manual by the way. It does not feel lazy or sluggish
Customer reply replied 2 months ago
The idle jumps up when ac is switched on normally
Nissan Mechanic: Jay, Nissan Technician replied 2 months ago

Sputtering is a sign of a Distributor or MAF sensor.

The idle going up when you use the AC is a indication the Idle Air Control system is working properly. It's suppose to raise the idle when the AC is on cause the AC is a load on the engine, so it wants the idle to be higher.

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Customer reply replied 2 months ago
Under load there is no sputtering...
Customer reply replied 2 months ago
when it starts you can smell it’s running slightly more rich
Customer reply replied 2 months ago
Funny thing.. just started the truck since last night and it’s running slightly rough at cold start just idling up for the cold start...
Customer reply replied 2 months ago
What about an o2 sensor?
Nissan Mechanic: Jay, Nissan Technician replied 2 months ago

Sorry, left work. I am now home..

02 Sensor if bad would cause a engine light, and really won't cause a running issue. It can cause the Running rich issue, but so can the Distributor and MAF sensor. Those two are the most common not to cause a engine light.

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Customer reply replied 2 months ago
Funny thing is sometimes the o2 sensor plug falls off and I get no cel.
Customer reply replied 2 months ago
Would the truck still drive normally Willy a bad mad or distributor and just idle rough?
Nissan Mechanic: Jay, Nissan Technician replied 2 months ago

Really? It should turn on the check engine light after a couple key cycles.

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Customer reply replied 2 months ago
It’s a one wire o2 sensor and ill plug it in and sometimes when I check the oil or what not is when I see the plug just dangling there and I’ll just plug it back in... my engine light works. Comes on when I turn the ignition on and goes out when truck is running. Why is that
Nissan Mechanic: Jay, Nissan Technician replied 2 months ago

Can't explain that with out checking it. Would need to see if the computer is reading the 02 sensor properly

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Customer reply replied 2 months ago
Unplugged maf. Truck idles at 750 but still rough.. also no check engine light
Nissan Mechanic: Jay, Nissan Technician replied 2 months ago

These computers don't read faults as fast as newer computers. It takes a few key cycles.

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Customer reply replied 2 months ago
Ok but it should not have idled exactly the same as if the maf was giving incorrect readings right?
Nissan Mechanic: Jay, Nissan Technician replied 2 months ago

So you would need to monitor the air and fuel trim readings with it plugged in and unplugged to see if it's metering air properly

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Customer reply replied 2 months ago
Any other possibilities of this rough idle and rich smell. Just want to have All available possiblikties
Customer reply replied 2 months ago
This is an obd1 how can o mI other that?
Nissan Mechanic: Jay, Nissan Technician replied 2 months ago

You would use the Diagnostic screw on the Ecm to check mode 3 for codes.

As for fuel trim readings, a gas analyzer would be required

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Customer reply replied 2 months ago
Do you have instructions on how to do that and also the code list?
Nissan Mechanic: Jay, Nissan Technician replied 2 months ago

Sure I have info on how you check for codes.. Hang on.

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Nissan Mechanic: Jay, Nissan Technician replied 2 months ago
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Customer reply replied 2 months ago
Do you think I could have sticking injectors? I did replace one a couple days ago because of a dead misfire at idle due to it being stuck open. I replaced that one and it solved that problem but could the others be starting to fail?
Customer reply replied 2 months ago
I just looked at the plugs and the cylinder with the new injector was white and clean and the others are slightly darker... what do you think?
Nissan Mechanic: Jay, Nissan Technician replied 2 months ago

Injectors are rare. But if you had one that was bad, then it wouldn't hurt to change them all I guess. How many miles on the truck?

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Customer reply replied 2 months ago
148000. The was that was bad was dumping too much fuel when plugged in. It would stop adding fuel if unplugged but once plugged in it would run smooth for a second and then drop that cylinder and you could smell raw gas out the tail pipe
Nissan Mechanic: Jay, Nissan Technician replied 2 months ago

If you had one bad injector doing that.. Then I would have changed them all

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Customer reply replied 2 months ago
Ok
Nissan Mechanic: Jay, Nissan Technician replied 2 months ago

So you may want to start there for your issue. I was unaware you had a bad fuel injector.

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Nissan Mechanic: Jay, Nissan Technician replied 1 month ago

If you have any more questions on this, please feel free to ask.

If not, and you're satisfied with my help, please RATE me by clicking the STARS on top of the page. That is how I get credit for my work. I hope I have provided you with Excellent Service.

Thanks Jay!

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Customer reply replied 1 month ago
I tried your suggestions and am having the same result.One thing I did notice is that the fuel pump seems to be loud. My truck has a slightly loud exhaust and at idle if you are standing at the passenger side bed area you can hear the pump buzzing away..Problem I am having is a idle with no load on engine it has a slight rough idle and slight smell of fuel from tail pipe.On a full tank of 87 octane I just barely make 200miles
Nissan Mechanic: Jay, Nissan Technician replied 1 month ago

The exhaust noise is most commonly a broken exhaust manifold bolt or manifold.

If the fuel pump is loud, you could be dealing with fuel pump failure and may not producing enough fuel pressure. I would also change the fuel filter as well and check fuel pressure. It should be at 36 psi

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Customer reply replied 1 month ago
I’m not worried about the exhaust noise, I have a replacement exhaust installed and it’s louder than the stock one. Was using it as a sound reference that I can hear the fuel pump over the noise produced by the exhaust.
Customer reply replied 1 month ago
I will check the fuel pressure later today but if the fuel pump was failing and fuel filter clogged wouldn’t the truck run rough while driving? Also wouldn’t I have less fuel instead of a Rich smelling exhaust?
Nissan Mechanic: Jay, Nissan Technician replied 1 month ago

Yeah.. The fuel pump should not be that loud..

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Customer reply replied 1 month ago
Truck drives fine accept at idle. Like it’s idling rich which is in turn causing the slight rough idle.
The idle isn’t terrible. It’s like a random slight misfire where you can see the engine shake off rythem and you can feel it in the body when your sitting in the truck and see the shifter shake when it happens...I had another Nissan pickup same engine and a friend has another that I can side by side compare and it didn’t run like this so I know it’s not normal.
I still have no check engine lights
Customer reply replied 1 month ago
What kind of miles to a tank is average. I’m not even driving hard, gradual acceleration shifting before 3k rpm and all I can squeeze out of this thing is 200miles and that’s pushing the fuel gauge below the white line... I don’t feel this is normal
Customer reply replied 1 month ago
I did replace all the injectors after our last conversation with All new ones.
Customer reply replied 1 month ago
New o2 sensor as well. I feel the issue is the engine is getting a little too much fuel which is causing the rough idle but what can cause that?On a side note I removed the egr and blocked off the manifolds and the terrible idle I had got much better due to it being slightly stuck open.
Nissan Mechanic: Jay, Nissan Technician replied 1 month ago

You removed the Egr? What is the rpm when the vehicle is idling?

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Nissan Mechanic: Jay, Nissan Technician replied 1 month ago

I do know that these older 2.4's are known to have the egr ports in the intake build carbon.

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Customer reply replied 1 month ago
I set it to the line under the 1000rpm line and it will float around there. Sometimes slightly higher some times lower. Never steady on the line... (new idle control valve installed as well)
Customer reply replied 1 month ago
I removed the egr valve, tube, everything. Blocked off the intake manifold, blocked the exhaust manifold, no vac leaks or anything.
Customer reply replied 1 month ago
No vac leaks that I could find at least
Customer reply replied 1 month ago
Tail pipe has black soot.
Customer reply replied 1 month ago
Truck is also manual transmission by the way.. any ideas?
Nissan Mechanic: Jay, Nissan Technician replied 1 month ago

Going to need a gas analyzer to measure the fuel trim to see if the car has a imbalance of air or fuel at idle to determine direction at this point..

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Customer reply replied 1 month ago
Ok, let’s say there is more fuel to air when this analyzer is used. What would the next step be?
Nissan Mechanic: Jay, Nissan Technician replied 1 month ago

If you are getting more fuel then air, that could be do to a MAF sensor not metering air properly

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Customer reply replied 1 month ago
I have actually swapped it with a known good unit from a friends truck with no change. What else could cause it to idle rich?
Nissan Mechanic: Jay, Nissan Technician replied 1 month ago

small vacuum leak

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Customer reply replied 1 month ago
How would I go about locating that?
Nissan Mechanic: Jay, Nissan Technician replied 1 month ago

That is tricky on these older cars. Pinch off lines and watch gas analyzer or use carb cleaner and spray is small sprays around intake and engine area's and if you see the engine idle change in a particular area, that is the leak.

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Customer reply replied 1 month ago
Wouldn’t a vac leak cause the engine to run lean at idle?
Nissan Mechanic: Jay, Nissan Technician replied 1 month ago

It could depending on where the vacuum leak is. But you need to really determine if your running rich or lean.

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Customer reply replied 1 month ago
She’s definitely running rich. Smell of gas, tailpipe gettin Black, and she’s burning a lot of gas
Nissan Mechanic: Jay, Nissan Technician replied 1 month ago

Could have a 02 sensor not reading exhaust gases properly

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Customer reply replied 1 month ago
Brand new o2 sensor installed a week ago
Nissan Mechanic: Jay, Nissan Technician replied 1 month ago

Could be a defective sensor a a catt converter causing the 02 not to read properly. Did you oscilloscope the operation of the 02 sensors?

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Customer reply replied 1 month ago
Same problem before and after the new o2 sensor replacement and this is obd1 with 1 wire o2 sensor before the cat. There is no secondary o2 sensor
Nissan Mechanic: Jay, Nissan Technician replied 1 month ago

Did you oscilloscope the operation of the 02 sensor

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Customer reply replied 1 month ago
Of a brand new o2 sensor, no I did not. It’s running as it did before I replaced the o2 sensor
Nissan Mechanic: Jay, Nissan Technician replied 1 month ago

We need a gas analyzer to see what is going on.

Maybe there is a restriction in the exhaust, or it's really hard to determine with out something to provide direction..

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Customer reply replied 1 month ago
If the intake manifold gasket is leaking would that cause it to run rich? Or have a slight rough idle? I did some reading and a lot of people have this issue of “blown intake manifold gasket” in the rear up near the fire wall. Have you ever experienced this?
Nissan Mechanic: Jay, Nissan Technician replied 1 month ago

Yeah, I have seen this where by the cylinder 4 intake the gasket breaks. But that would force a lean condition, but also a stumble at idle only.

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Customer reply replied 1 month ago
It only has a slight rough idle. Going to pick up some carb cleaner. Only had a little brake cleaner and I hit the area and I thought the idle dropped but I ran out
Nissan Mechanic: Jay, Nissan Technician replied 1 month ago

ok

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Nissan Mechanic: Jay, Nissan Technician replied 10 days ago

If you have any more questions on this, please feel free to ask.

If not, and you're satisfied with my help, please RATE me by clicking the STARS on top of the page. That is how I get credit for my work. I hope I have provided you with Excellent Service.

Thanks Jay!

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