Idle , hesitation problem 2000 sentra

[mmm_2000]

Here is a quick history of my car:
2000 sentra 1.8, AT, i have 82k miles on it

- replaced battery at 54k (that's when i purchased the car)
- replaced rack-pinion unit at 65k (leaking)
- replaced front pads and rotors at 70k
- replaced alternator just a few months ago at 80k (the diodes went bad as I got a "diode ripple" problem on a electrical tester)
- regular maintenance done by the manual
- I also have a K&N air filter installed and I serviced it regularly

So a few weeks, maybe up to 6 weeks ago I started to notice a problem with the idle and the problem is present since :

I am stopped at a light, car in "Drive" and I notice that my rpm goes from like 700 ( the regular rpm for that situation) down to like 300-400rpm just for like 3-4 seconds and I also feel some vibration coming from the engine and then it goes back to normal.

Then after exactly 30 seconds it does it again, but I only feel it when stopped and the engine is at idle or low rpm.

Its weird cause that variation in rpm comes every 30 seconds ! If I turn the AC on, the cycle is broken and it would not do it again until after a few minutes and then it starts again ! The same 30 secs !

This problem appears even when the car is in P (park) !
I spent about 1 hour in my garage examining the problem at idle !

Let me remind u that the car runs perfect otherwise.

And the problem only appears after the engine got to the normal operating temperature. Not when its cold.

In the manual it says I have to replace the spark plugs at 105k miles, so i have not replaced them yet !

There is no engine light or anything on while the car is running. Its just normal except that variation in rpm every 30 seconds.
And a few times while stopped at a light the rpm went so low that the engine died while the car was still in "drive". Then it started right back without any problem after cranking it. Cold starting is also perfect, I only have to crank it for like a second to start when the engine is cold.


Could it be a problem with the ignition coils ?? (it has one coil for each plug)
What could be the cause for that rpm drop ? Maybe the mass airflow sensor or some of the oxygen sensors (it has 4) ??
Should I ask a friend of mine to connect my car to a code reader ( He owns a repair shop), but there is no engine light or anything on. Is that code reader going to be able to pinpoint the problem ? i have not called him yet cause he is always very busy at the shop, but I will if I think he will be able to help me with that code reader.

Please help me cause I have a trip to Vegas coming up and I don't want to get stuck on the road !!!

Thank you

[nismo_pilot]

check your idle air control valve, maf, and possibly plugs but i listed them in order of importance

[slideways...]

ummm you may have an ECU problem. try pulling the battery for 10 minutes, then reconnecting it, take your car out and beat on it for 10 minutes. that may help or it may not if theres a physical ECU problem. if your plugs are good i would look into getting a mechanic to look at it. ECU problems are hard to diagnose.

[nismo_pilot]

true slide..... it may also help to reset the program your car uses for the IAC but you should prolly pull it off the throttle body and look at it/clean it if you can

[mmm_2000]

k, two years later, 15k miles more and the problem is still here.

It was having the symptoms once in a while, i had a few weeks when the problem was not even there.

This week I replaced the IACC and $130 later after several hours of works, guess what?? Nothing changed. The problem is still there.

Now I'm desperate because even if I have the AC on it still shuts down at idle after the 30 secs cycle. And yes, I drove the vehicle for so long with this problem, but having the AC on at all times it solved the problem, till now. I'm stuck.

So yesterday I take my car to a very good repair shop here in my area and Tony, the mechanics name, spent I think about 3-4 hours on it without being able to figure out what the problem is.
He told me it might be my remote start alarm. Tomorrow i'm taking the car back to him.
I disconnected my remote start from the car and guess what?? Nothing changed. The problem is still there.

Lately its been so bad that every stoplight the car dies. So I put it in neutral and hold the gas pedal so the engine wont stop. That's how i'm driving my car back and forth...

He also said it might be the ECU so he will do more testing tomorrow.
He tested the MAFS and it works fine. I asked him what about the TPS and he said is not very likely.

And still no check engine light on. At least now I know not to ever ever buy a nissan again.... Im going to get a Honda or a Toyota in the future, but now I have to fix this peace of junk...

Anybody have any ideas?

[consultIII]

can you get a scanner and view live data. Hard to know with out information. If you can get one; here is what to do.

view iac counts and fuel trim.
sounds like a fueling issue not spark....why...doesn't happen cold in open loop (engine not using o2 data and idle speed is higher).

Also a/c engagement will demand a higher iac opening position.

View fuel trim...nissans read as 100% as ideal (at least with factory consultII scan tool)...readings more than +/- 10% indicate a fuel control issue possibly relate to maf (you stated you installed a K&N filter...nissan maf sensors are very sensitive to contamination...they don't have a burn off circuit...if you installed a wet filter (oiled) the oil has contaiminated the maf. Aftermarket air filters are bad as they don't filter fine enough. Never put anything but a factory air cleaner in a Nissan. Otherwise will wreck the maf which is a $400 part (in Canada are cheaper in USA). Open the air filter and wipe your finger across the mesh screen before the maf. If you can wipe off residue the maf is dirty...you can try maf cleaner spray but it may not recover.

check for vacuum leaks...view trim at idle if no good rev engine to 2000rpn and keep it there and see if fuel trim comes back in spec if yes you have a vacuum leak. locate leak by spraying around intake with brake cleaner...when idle changes you have located the leak...inspect the air snorkel for cracks or leaks that occur before the maf

If trim ok check iac counts... should be within 5 - 50 counts

let me know what you find

[mmm_2000]

Originally Posted by consultIII

can you get a scanner and view live data. Hard to know with out information. If you can get one; here is what to do.

view iac counts and fuel trim.
sounds like a fueling issue not spark....why...doesn't happen cold in open loop (engine not using o2 data and idle speed is higher).

Also a/c engagement will demand a higher iac opening position.

View fuel trim...nissans read as 100% as ideal (at least with factory consultII scan tool)...readings more than +/- 10% indicate a fuel control issue possibly relate to maf (you stated you installed a K&N filter...nissan maf sensors are very sensitive to contamination...they don't have a burn off circuit...if you installed a wet filter (oiled) the oil has contaiminated the maf. Aftermarket air filters are bad as they don't filter fine enough. Never put anything but a factory air cleaner in a Nissan. Otherwise will wreck the maf which is a $400 part (in Canada are cheaper in USA). Open the air filter and wipe your finger across the mesh screen before the maf. If you can wipe off residue the maf is dirty...you can try maf cleaner spray but it may not recover.

check for vacuum leaks...view trim at idle if no good rev engine to 2000rpn and keep it there and see if fuel trim comes back in spec if yes you have a vacuum leak. locate leak by spraying around intake with brake cleaner...when idle changes you have located the leak...inspect the air snorkel for cracks or leaks that occur before the maf

If trim ok check iac counts... should be within 5 - 50 counts

let me know what you find

K, I bought an obd2 interface for my laptop and hooked it up and I drove for about 10 mins and recorded live data.
My Long trim Fuel is pretty much all the time at between -20 and -25 or around there except under very hard acceleration when it increases to almost positive levels.
The Short trim is mostly negative and it only goes positive under hard acceleration.

I will check for vacuum leaks and I will check the MAF.

Another weird symptom here. Once the engine is warm, in P or N I cannot accelerate anywhere between 1500rpm/5000rpm. If I only accelerate a little (lets say trying to aim for about 2000 rpm) the rpm jumps up and down fast between 1500 rpm and 1800 rpm. I accelerate further, still the same jumping up and down of the rpm in the same range. I go further down with the pedal and then the rpm jumps to over 4000 and then within half a second it falls down to the same range 1500-1800 and it keeps on bouncing up and down. It is really frustrating right now...
Here is the video I recorded:

http://www.youtube.com/watch?v=BRA8YSTYe5I

Also, the MAF readings seemed to go along with my accelerator (more pedal more gals of airflow per minute) so maybe my MAF is not bad...
And also my exhaust smells like when a vehicle it just started, even if I just drove it for 30 mins, so I think its running rich.

I still have to analyze more the data I recorded on my laptop through the OBD.

Still no check engine light on. Any ideas?

[mmm_2000]

So if I record live data, what should I do? Drive the car around, or just record the idle data? What kind of drive test should I record. I want to post the live data here, maybe you guys can help me.

I think the absolute TPS readings don't make too much sense, but I will analyze them further later.

I also have a 2001 accord 2.3l. Should the absolute tps / maf readings be about the same for my sentra and my accord under the same simulation? I'm thinking in recording the accord live data and compare it to the sentra. The accord runs perfect. I am not sure how to interpret the data I'm getting. Still researching.

[mmm_2000]

Well, many people have said K&N filters and the oil you treat them with can cause a MAF to fail but here is what K&N said:

http://www.knfilters.com/maf/MAFTestresults.htm

Should we believe them? I think we should because they are big, and if someone could prove that their filters treated with oil damage the MAFs thatn they would be out of business.

[consultIII]

Your car is running rich. the ecm is reducing fuel so much that it is at its adaptive limit and can't cut fuel anymore as evidenced by the trim numbers you have reported.

The reason the car runs ok when cold is that its ignoring the 02 sensor until it comes up to temp and goes closed loop. Which leads me to believe you have a bad o2. to verify check 02 sensor switching at 2500rpm. Does the pre cat 02 switch fast and vary from 800mv to 200mv. Post the video of your datastream of that on utube. Run the car with the 02 unplugged; does it run better?

Also, the 02 sensor is ignored at wot. Does the car run ok at wot?

if that is ok; check fuel pressure for being to high and make sure the fuel pressure regulator vacuum line is connected and can pass vacuum.

In park or neutral you get fuel cut off at higher rpms due to no load on the engine.

You can believe what you want about k&N (or any dry or wet aftermarket filters put on nissans). I've seen it at the dealership level for years at nissan. May not effect other car brands MAF as bad; they may have burn off circuts. What do you think K&N is gonna say? Has any manufacturer advertised to not use their product? Do what you want, its your $400 maf sensor. Leave it in and eventually we'll both know what happens.

have never heard of absolute tps...do you mean absolute manifold pressure?
map on most 2000's and later nissans is not used for primary drivability or fuel control but rather testing purposes ie. i/m monitors

[mmm_2000]

Originally Posted by consultIII

Your car is running rich. the ecm is reducing fuel so much that it is at its adaptive limit and can't cut fuel anymore as evidenced by the trim numbers you have reported.

The reason the car runs ok when cold is that its ignoring the 02 sensor until it comes up to temp and goes closed loop. Which leads me to believe you have a bad o2. to verify check 02 sensor switching at 2500rpm. Does the pre cat 02 switch fast and vary from 800mv to 200mv. Post the video of your datastream of that on utube. Run the car with the 02 unplugged; does it run better?

Also, the 02 sensor is ignored at wot. Does the car run ok at wot?

if that is ok; check fuel pressure for being to high and make sure the fuel pressure regulator vacuum line is connected and can pass vacuum.

In park or neutral you get fuel cut off at higher rpms due to no load on the engine.

You can believe what you want about k&N (or any dry or wet aftermarket filters put on nissans). I've seen it at the dealership level for years at nissan. May not effect other car brands MAF as bad; they may have burn off circuts. What do you think K&N is gonna say? Has any manufacturer advertised to not use their product? Do what you want, its your $400 maf sensor. Leave it in and eventually we'll both know what happens.

have never heard of absolute tps...do you mean absolute manifold pressure?
map on most 2000's and later nissans is not used for primary drivability or fuel control but rather testing purposes ie. i/m monitors

First of all I really appreciate you trying to help me and maybe others.
Now back to the issue:

I have 4 o2 sensors. 2 before and 2 after the cat. They are regular o2 sensors, not wideband. Should I disconnect them one by one and see what happens?
Under hard acceleration the car runs fine. It has plenty of power. No problem here. Also on the freeway or just on any normal road it runs perfect. At least it seems normal to me.
I get a little hesitation when the engine is cold if I try to accelerate hard in the first gear. If I go slow on the pedal there is no hesitation. Once is warm (within 2-3 mins after I start in the morning) there is no more hesitation.
Other than that the car runs fine on the road, except at idle.

I also noticed the long and short fuel trim get closer to normal while cruising and the short trim is very bad (-25%) at idle only.

I disconnected the vacuum line at the fuel press regulator and the rpm goes up when I do that. I don't have a fuel pressure tester, but I'll try to get one.

The software I'm using its called PCMSCAN and the tps data is listed as "absolute throttle position":

http://www.palmerperformance.com/pro.../data_view.png

When you say to check the o2 sensor switching at 2500 do you mean I have to do it in P or N or while driving?
In P or N I won't be able to do it because I am not able to hit the rpm I want, because it cuts off like you said. So I guess I'll do it while cruising.

I think you convinced me on the K&N thing. I will go back to the regular air filter. (here in California I can buy the MAF for about $215, but that is still a lot of money for me ! )

Is it normal to have the fuel cutoff when I'm in P or N?

I will get the recorded data up on utube, soon !

[mmm_2000]

Today after driving the car for about 20 mins from work I disconnected the o2 sensors one by one and I noticed that if I disconnect both top o2 sensors the car seemed to run fine at idle without shutting down or drops in rpm every 30 seconds.
If I disconnect all four it also runs fine at idle.
If I disconnect only the two on the bottom then the car still has the idle problem every 30 seconds.

So once the top two are disconnected the car runs fine! What does this mean?

Can the fuel pressure regulator still be the problem? Or is it 100% sure my top 2 o2 sensors are bad?

Tomorrow I will buy a o2 sensor socket and a torch and I will bench test the o2 sensors just to be sure.

If the sensors turn out to be good then I'll have to test the fuel pressure and the fuel pressure regulator.

[mmm_2000]

K, I tested all 4 o2 sensors and they are all fine. I unplugged the booster vacuum line and once I do that the voltage drops to zero. And I can control the voltage with the amount of vacuum I let slip into the intake. That's how I tested them.

My voltmeter showed the voltage drops when the line was disconnected.

Now what?
I am still running very rich and the o2 voltages are steady on all 4 o2 sensors at around 0.9v. I'm afraid I'm going to damage the cat and/or the o2 sensors if I keep on driving so rich...

Any ideas?

[consultIII]

3 things can cause this rich condition
high fuel pressure
bad pre cat o2 sensors
bad maf

need a gauge to check fuel pressure.

b1s1 and b2s1 o2 sensors checks are best done as per previous post in closed loop operation. Watch for fast transision from high to low volts. (creating a vacuum leak will cause the low voltage reading...but a lazy or askew 02 sensor would pass this test). You don't need to test post o2 as they are only used to testing the cat operation; not fuel deliery.

typically contaiminated maf overcompensate fuel at idle (rich) and undercompensate at 2500rpm (lean). bad maf effects both bank fuel trim. maf are best diagnosed watching fuel trim at idle and 2500rpm.

I like the if in doubt take it out. you can try it will the maf also. start the car, unplug the maf and see what happens. Note the car may stall when you unplug the maf; if it does disreguard the test as it means nothing diagnostically. If it runs fine then maybe bad maf.

[mmm_2000]

Originally Posted by consultIII

3 things can cause this rich condition
high fuel pressure
bad pre cat o2 sensors
bad maf

need a gauge to check fuel pressure.

b1s1 and b2s1 o2 sensors checks are best done as per previous post in closed loop operation. Watch for fast transision from high to low volts. (creating a vacuum leak will cause the low voltage reading...but a lazy or askew 02 sensor would pass this test). You don't need to test post o2 as they are only used to testing the cat operation; not fuel deliery.

typically contaiminated maf overcompensate fuel at idle (rich) and undercompensate at 2500rpm (lean). bad maf effects both bank fuel trim. maf are best diagnosed watching fuel trim at idle and 2500rpm.

I like the if in doubt take it out. you can try it will the maf also. start the car, unplug the maf and see what happens. Note the car may stall when you unplug the maf; if it does disreguard the test as it means nothing diagnostically. If it runs fine then maybe bad maf.

K, I checked the readings from the maf at idle. Nissan specs from the service manual says, at idle, warm engine Maf should read between 1-4g/s of air. Mine reads about 6-7g/s at idle. So I went and bought a maf from Kragen Auto, my cost 250 + core. I put it on and the engine runs perfect !!!! I stayed at idle for about 10-15 mins, engine feels great, no hesitation, fuel trims are perfect and the short trim is at around zero most of the time plus or minus 2-3%. I was so happy. i drove it arounf for another 10 mins up to freeway speed. And here is the "surprise":

Next day I try to start the car to go to work and the engine runs really really bad, idle jumps up and down from 300 rpm to 800 rpm and engine stalls after after like 10 seconds. I was so upset. Check engine light came on (p0100 - maf malfunction) as I checked it later in the day. How can a Maf go bad over night, with my car in the garage. Also here the temperature doesnt drop in the night below 50 degrees. I was getting late for work so I try to drive the car and I could not get the car at a higher speed than 30-35mph. So I dragged myself to work, knowing the auto parts store is next door and I can get a warranty replacement.

I got another Maf from the parts store after work, and with this same thing. I can barely keep the engine running, trying to rev it all the time and it chokes and so on. So then again I barely drive the car back to my house and I put my old Maf in and my car now works like before. But at least is driveable. Still rich at adle. I reset the check engine light and with my old maf it doesnt come back on.

Now I ordered a different brand maf and we will see if this works: beck/arnley. The original brand was Cardone. They are all remanufactured. The new one is about $430 !!!!!

Is it possible that the maf I bought went bad over night ???
And is it possible that the second one was bad out of the box???
My problem has to be the Maf, right ? With the first one my engine ran perfect, like it didnt in years. Perfect.


Im frustrated....

Tomorrow I'm receiving the other brand Maf and I'm going to exchange it again. Ill post as soon as I have the results. I also bought a stock air filter and Im not using K&N anymore.