2001 QX4 Engine Light, P0505, and P0420

[KellyBoston]

I have spent the last 12 hours searching back thru old posts to try I get an answer. My Qx runs ok, but is consuming oil, and horrible gas mileage. I'm sure it's due for a tune up, and fuel filter. I have changed oil and air filter, I want to know If I should tune, and perform maint. First, then address these, or vice versa? Also want to make sure I'm no going to do any serious damage driving with these codes.

I'm going to add chevron techron/redline sl1 to fuel, clean throttle body, check vacuum hoses, and clean maf today if your feedback indicates it wouldn't hurt! It will take a few weeks before I can afford a tune up, as Next Week is Spring Break in KY.

Please advise on what to do first!!

01 QX4 153k 4x4 3.5l

[Towncivilian]

Try all the things you stated first, that sounds like a good start. Is your idle OK?

[KellyBoston]

I'm having the same issues as several others upon starting. Cold crank in the morning, I have to give it has to keep it running for first 5-8 seconds, or just shift in to gear, or it dies. Then it's fine the rest of the day.

Also about 3 months ago, I drove to work and it did fine. When I left work 5 hours later, it wouldn't idle at all. I had to give it gas to keep it running at redlights. I took it to a local shop, the nut that holds the accelerator cable had backed out causing it not to idle. He set my idle to 500 originally and I noticed no power, so I called him and he told me to adjust it to 1000rpm. I understand that it should be 650-750 though right??

[Towncivilian]

Yes, idle at operating temperature should be 750 +/- 50 in neutral.

How was idle adjusted? ECU should control the idle, there is no idle adjustment screw if I recall correctly.

[KellyBoston]

Yes,(excuse my lack of terminology) but the cable from accelerator pedal and cruise control cable on top in the intake...they are wound around in cirlces with a spring that connect to the piece that can open the throttle. (How u can rev engine from engine compartment) there is a 7mm but that can be loosened, and there is a set screw that u can set as a stopper. only allowing the piece that opens the throttle to rest at a certain spot. By unscrewing it, it doesn't let the flap s*** all the way, this increasing idle.

That's how the mechanic adjusted it. And then that how I adjusted it from 50 to 1000.

[KellyBoston]

That is a 7mm NUT not but....and I thought I typed that unscrewing the set screw to not let the flap SHUT all the way! Guess i hit i instead of u! Lol. Funny how it sensored it lol!

[jubal82]

Hi Kelly,

Did that quick fix by your mechanic solve the issue of the low idle problem in the long run? My car is acting the same way so I am thinking about doing the same thing as you did. I just want to know how it kept up for you.

My car is also having the crank start problem as well
Any insight would be appreciated much.
Thanks,

[Buzzman]

Ok, so where do I begin?
I started having this problem last November, and have gone through a lot of trouble, learning, and money, before I was finally able to fix it.
In a nutshell, If you are getting 505 codes, or 500 codes, then your IACV has failed, and has taken your ECM with it.
Even if you are not getting these codes, I can assure you with 99% accuracy that this has happened to you (bad IACV I mean).

OK, a little lesson on how the system works:
Firstly, the ECM, throttle position sensor, and IACV sets the idle speed. There is NO mechanical idle adjustment.
When the engine is operating and idling normally, the main throttle valve is fully closed (i.e...your foot is off the gas pedal).
The engine still needs a little air for it to be able to idle though, and it gets that air via the IACV valve. That is it's job.
The IACV opens and close accordingly, letting in more or less air, depending on how cold the truck is.
On cold startups for example, the IACV opens up a little more, lets in more air, and therefore the truck will idle a little faster when cold.
As it warms up, the IACV closes up a little, lets in less air, and the idle drops to normal.
When the IACV fails, it fails in the closed position, and your engine gets no air, and it stalls. That's why you have to keep your foot on the gas pedal a little.
Your engine is starved for air.
Tightening up the throttle cable until it idles is not a fix. It only masks the problem.

Now for the fix: A new IACV, and a new or rebuilt ECM.
The IACV is around $400, and a new ECM from the dealer is over $1000.00
The good news is, there's a company in South Carolina that repairs them for this exact problem. Flat rate of $250.00
They are Circuit Board Medics.
That's what I did with mine....got it fixed.
It may be tempting to try and get a used IACV, or maybe pull one from a junker, but I caution against doing that.
If you install a used one, and it's no good, you'll blow the ECM again. Bite the bullet and get a new from from Nissan.

If you still need more info, check out this thread:
2002-pathfinder-wont-idle-any-suggestions-t530479.html

[Greilly]

Same issue as stated in the last post. Send ECM to DAT in Riverside CA. Ordered OEM IACV from infiniti today and will install next Thursday. Has anyone been successful with this in the past? And any tips for installing the IACV??

[Buzzman]

Check the thread that I highlighted in the previous post.
Everything you need to know is written up there.
Good luck.