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Discussion Starter #1
Hi there, I have a
2001 Nissan Altima GXE Limited Edition 2.4L (automatic) 136,034mi.

I've been having problems for a while now that I can't figure out. Also, when it comes to mechanical problems (and I mean ONLY mechanical, not electrical or computer programming) I prefer to do things myself if at all possible in my shitty apartment complex.

Anyways, the main issue I have is my idle.
ONLY when the engine is nice and warm do these problems occur. 2/3 problems are infrequent, but on a regular basis:

1. IDLE: (constant) my idle is really messed up. (With AC running) in park I currently have my idle set to 1500 RPMs to circumvent this issue as a temporary fix. My idle erratically dips (and periodically) rises when I'm not driving (fir example at a stop light). If I'm running the AC (not just the blower) the dips can be as extreme as a 700 rpm drop. With the adjusted idle, while in drive my RPM's are at 1000, and periodically dip to about 800. Infrequently, (using when I start driving) my idle will increase by about 500-1000 for seemingly no reason at all.
Then, while in drive, my idle gets stuck (and continues to act erratically) ONLY between 39-50mph. If I drive at 51mph or higher there are absolutely no issues at all.

2: ERROR CODES (infrequent) I'm pretty sure I have to replace my catalytic converter. Every week I receive (and clear) a bank 1 P0420 error code. What's puzzling though is sometimes it's clear for 5min, 1 hr, a day, a few days, or even a week before coming back on. In theory, after clearing the code (and assuming my cat is in fairly bad shape at this point) I should get the error code back every time I start driving after clearing it.
Finally, (very infrequently) I also receive a P03? Cylinder 1 Misfire code reading. It might occur once in a week or two, or sometimes only once in a month.

I have replaced:
My Air Filter (multiple times, with varying brands)
My Throttle Position Sensor (TPS) based on a recommendation from a few people.
Also had my oil change done

At this point, mainly due to inconsistency with the error codes, I'm wondering if anyone has an idea what's wrong with my 2001 Nissan Altima GXE Limited Edition 2.4L (automatic)..???

Thanks in advance.
 

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I bet a big portion of your trouble is you resetting the idle too high MECHANICALLY to interfere with your electronic engine control which is ALWAYS trying to lower the idle speed back down to the OEM software decreed number, which will be lower than the numbers you quote there. When you get the mechanical idle setting out of a range the ECM expects to see there will always be trouble of the type you describe as the ECM sees what you have done as wrong and tries to correct it.

If the idle was dropping low enough before to try to die before you bumped idle speed up you have to address the issue of why it was trying to die, bumping idle up is not a solution and only makes it worse.

If your cat is dead enough (clogged) then exhaust stacking up in it can occasionally make a cylinder misfire when the back pressure at some point backflows exhaust back into a cylinder at overlap. Exhaust will not burn again and then you get a slow burn misfire due to the patchy mixture that is already partly burned.

You people that continue to drive forever instead of fixing the cat, are only abusing yourselves and the cars, the cars don't care and will simply run like crap regardless of what you want. Nothing personal intended there at all, it's just that a spate of people asking why this or that problem is happening are driving cars around with dead cats on them and wondering why things are going wrong. A dead cat is not a benign event.

Many codes have certain criteria to hit before they show back up, they do not come back on immediately based on the software count needed to retrigger it. Depends on how the software is written.
 

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Discussion Starter #3
I bet a big portion of your trouble is you resetting the idle too high MECHANICALLY to interfere with your electronic engine control which is ALWAYS trying to lower the idle speed back down to the OEM software decreed number, which will be lower than the numbers you quote there. When you get the mechanical idle setting out of a range the ECM expects to see there will always be trouble of the type you describe as the ECM sees what you have done as wrong and tries to correct it.

If the idle was dropping low enough before to try to die before you bumped idle speed up you have to address the issue of why it was trying to die, bumping idle up is not a solution and only makes it worse.

If your cat is dead enough (clogged) then exhaust stacking up in it can occasionally make a cylinder misfire when the back pressure at some point backflows exhaust back into a cylinder at overlap. Exhaust will not burn again and then you get a slow burn misfire due to the patchy mixture that is already partly burned.

You people that continue to drive forever instead of fixing the cat, are only abusing yourselves and the cars, the cars don't care and will simply run like crap regardless of what you want. Nothing personal intended there at all, it's just that a spate of people asking why this or that problem is happening are driving cars around with dead cats on them and wondering why things are going wrong. A dead cat is not a benign event.

Many codes have certain criteria to hit before they show back up, they do not come back on immediately based on the software count needed to retrigger it. Depends on how the software is written.

Thanks. At first it felt personal, but I figured out how you meant that response.

And yes, my idling was already erratic before I increased it myself. If I were to set it back to normal I suspect the problem would get worse.

Here's an update though, and a weird one at that. I had my P0420, and P0300 (new) codes today. I had to get on i95 to get home from work, due to very slow traffic as a result of horrendous rain.
I did NOT clear the codes... but my DTC light just magically VANISHED when I got to my exit... if that helps with anything.

Also, when my paycheck hits I'm going to get my cat serviced as soon as possible, and also replace all 4 of my spark plugs with the new (front) cat installed.
I live in Florida, so I'm also replacing the rear cat with a straight pipe just on the offhand chance the rear cat is also bad. I'll definitely provide an update afterwards.
 

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Some DTCs can reset if they perceive the issue is gone. Again depends on how the software is written.

And thanks for not freaking out to take things personally. Not meant that way at least here. I try to fix drivers as much as cars and sometimes you have to be blunt, more than I'd like but would people rather me let them motor on in blessed ignorance? Most will say yes out of pride but secretly not wanting to stay stupid, it being the cause of a lot of effort say in job pay given to some mech who thinks you are moneybags. They never pay you enough at work, better to try to get some of it back from the repair shop I think.

How I have kept 3-4 cars running at all times for over 45 years now and never paid for any car repair ever doing it. Sooner or later I'll get bit but not yet. Saved thousands along the way.
 

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Discussion Starter #5
Some DTCs can reset if they perceive the issue is gone. Again depends on how the software is written.

And thanks for not freaking out to take things personally. Not meant that way at least here. I try to fix drivers as much as cars and sometimes you have to be blunt, more than I'd like but would people rather me let them motor on in blessed ignorance? Most will say yes out of pride but secretly not wanting to stay stupid, it being the cause of a lot of effort say in job pay given to some mech who thinks you are moneybags. They never pay you enough at work, better to try to get some of it back from the repair shop I think.

How I have kept 3-4 cars running at all times for over 45 years now and never paid for any car repair ever doing it. Sooner or later I'll get bit but not yet. Saved thousands along the way.
Good evening/morning.

I hear that - seriously, I do. Most of my delays in vehicle repairs just boils down to lack of money. Saving you a really long sob story; I'm 25 with no family in the country, about 18k in debts that's killed my credit. So, I've been busting my rear trying to chip away at that debt, pay my bills, and rebuild my credit pretty much completely by myself.

Back to the car, I knew she had a handful of issues that needed some attention, but fact of the matter is that repairing that cat is going to max out my shitty credit card again, which is going to take me another 2-3 months to pay off. I do what I can, when I can, but it ain't much.

As previously mentioned, once I have the catalytic converter and spark plugs replaced, I'll give an update on the RPM issues.

Meanwhile, it'd appear my car adjusted itself and set the RPM's back to default (I'm not sure if that's even possible, or if my idle is FUBAR at this point, causing it to drop back down to 'normal'). When I have the cash for it I'm also going to replace the fuel injectors (regardless whether it's needed or not),and I definitely don't have a vacuum leak either. I used the 'cigar trick' (with my vape due to MUCH more smoke) and there isn't one.
 

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Discussion Starter #6
UPDATE (June 14)

So, I haven't replaced the cat yet. BUT I switched out the spark plugs with new ones without any change in my idling.
Today, I noticed something... peculiar... playing around with the idling, trying to find a leak, noise, or something else...
...I THINK my motor mounts are... well... not to put too fine a point on it... F**KED.

I used a 20" extension bar fir my 1/2" socket to hold the brakes, so I could put my car in drive to mimic the idle issues I've been having, and I noticed my entire engine moving every time I switch between P/R/N/D/2/1. Some of those were really significant P-->D was about 2-3" of movement.

Any advice, and could this create slack in my belt, causing the idle issues (a suggestion from my uncle)?

What should I replace first - engine mounts, or the cat?

Thanks...
 

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09 Altima 3.5SE 6MT Sedan
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If your mounts are that bad...then driveability will improve a lot by changing them. If money is tight...fix the emissions stuff first.
 

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Discussion Starter #8
If your mounts are that bad...then driveability will improve a lot by changing them. If money is tight...fix the emissions stuff first.
My emission/idling issue seems on the border of being resolved though. Still kicks a little bit at a complete stop in D, but after adjusting the RPM's back down I can drive normally.

Think I should still replace the cat first? I'm leaning towards the mounts because is more expensive, and I could replace the cat a week later.
 
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