Engine Surging in P and N and wants to stall in D

[Suave91]

I have a 2001 qx4 and it stalled and died the other day in traffic. I was able to fire it back up and keep it running by keeping my foot on the gas. When I put the car in neutral the engine surged between 1100rpm and 2100rm (in park it was about 1400-1900rpm). I parked it at work and when I drove home it idled and drove fine. Later that night the same thing happened. I scanned it (the service engine soon light was not on) and it gave me a P0505 code. from what I've found on this people only had the stalling part, no issues with surging. So far the only suggested fix I found was replace the IACV and the ECM both of which need to be replaced together because one shorts the other out. Since they are pretty expensive I want to be sure this is the problem. Any help is appreciated.

ps ive been told I can manually raise the throttle to limp it by until the parts get in. Does anyone know if I need to unplug the IACV when i do this

[nickelghandi]

As far as that being your issue, I am not sure, sorry.
However, if you have a cable driven throttle and are not drive-by wire, you can adjust your throttle position sensor to have it idle higher. Google the part and you will know it when you see it under the hood. It is near the intake manifold.

[Buzzman]

I have a 2001 qx4 and it stalled and died the other day in traffic. I was able to fire it back up and keep it running by keeping my foot on the gas. When I put the car in neutral the engine surged between 1100rpm and 2100rm (in park it was about 1400-1900rpm). I parked it at work and when I drove home it idled and drove fine. Later that night the same thing happened. I scanned it (the service engine soon light was not on) and it gave me a P0505 code. from what I've found on this people only had the stalling part, no issues with surging. So far the only suggested fix I found was replace the IACV and the ECM both of which need to be replaced together because one shorts the other out. Since they are pretty expensive I want to be sure this is the problem. Any help is appreciated.

ps ive been told I can manually raise the throttle to limp it by until the parts get in. Does anyone know if I need to unplug the IACV when i do this

OK, the 0505 code is definitely the IACV going/gone bad.
You need to replace it IMMEDIATELY, before the ECM craps out.
The fact that the engine will still idle and surge when not in gear tells me the ECM is still communicating with the IACV and trying to set it right.
If you continue to drive it with the bad IACV, the ECM will eventually conk out, and then the engine will stall out and not idle, period, no matter what gear you are in.
Trust me, I've been through this.
I p****d around and tried a whole bunch of other stuff before my truck finally decided never to idle again.
By the time I realized my IACV was bad, it was too late to save the ECM.

As for temporarily adjusting the idle, yes, it's possible.
You can adjust the throttle cable so that it holds the throttle butterfly valve slightly open in idle mode.

If you are going to wait with any repairs, then yes, I believe you can unplug the IACV.
That way it won't communicate with the ECM, possibly saving it (no guarantee).
Not sure what will happen though. It probably won't idle if you unplug it.

Either way, get a new IACV as soon as possible, limit your driving in the meantime, and replace it as soon as you can.
Unplugging it and then adjusting the cable just covers up the problem, and should not be a permanent fix.

[Suave91]

Ok, Ill order the IACV today and unplug the one in the truck and see if i can manually adjust the throttle to make it idle until it gets here. Are you sure its not a vacuum leak issue? Just want to be sure I check the cheaper stuff first. And due to my symptoms you believe me ecm is still functioning properly and hasn't shorted yet? Thanks a lot for the reply

[Suave91]

*update* Just unplugged the IACV and it revs high (assuming it just stuck open). But it still surges in park and neutral.

[Buzzman]

The fact that you are getting a P0505 code is the key.

If there were no fault codes, then I would pursue the vacuum leak checks, etc.
A flaky MAF sensor, tps sensor etc., can also cause erratic idling issues.
Non of these things will trigger a 0500 series fault code though.

After my experience with this issue last year, I still recommend changing out the IACV.
The other reason for going that route is just the age of the truck.
After 13 years of use, the IACV is on it's last legs, regardless.
Pay now, or pay later.

[Suave91]

Ok, should i just bite the bullet and pay for the ecm as well or risk shorting the new iacv? and since ill be replcing them should i reconnect the old one and mess with the idle until the new parts get here? rock auto has re-manufactured ecms for about 300 bucks

[Buzzman]

Here's a link to the original thread that started a few years ago re: IACV going bad, etc. It's worth a read:

2002-pathfinder-wont-idle-any-suggestions-t530479.html

There are ECM repair Companies out there that will fix the P0500, P0505 problem for less than a rebuilt ECM.
Buying another ECM means you also have to go through the hassle of re-programming your key fobs etc. PITA.

I sent my ECM to circuit board medics in carolina (if memory serves). They repaired it for a flat fee of $250.00.
They also turned it around in two days. Very good service.
There are others out there as well that may be cheaper.

As for the surging, you may have a MAF sensor issue as well.
Take it out and clean it. Also, try running while it's unplugged.
A new MAF for the 2001 can be had fairly cheaply if you order one for a 2001 Maxima. Same MAF, at a third the price.

[Suave91]

Yea I heard about that place. The only problem is I'm in canada so the shipping costs would make it the same or more than a remanufactured ecm. Plus if I order a remananufactured one I can still drive the truck if I need to where as if I sent my ecm out I'd be stuck. Thank you very much for all the help

[Buzzman]

The only problem is I'm in Canada so the shipping costs would make it the same or more than a remanufactured ecm. Plus if I order a remananufactured one I can still drive the truck if I need to where as if I sent my ecm out I'd be stuck.

Hey, I know what you mean. I'm in Ottawa (go Sens, Leafs suck).
I had the same concerns. Fortunately, we had a three week vacation in Florida planned when this happened.
I parked the truck in my garage, took out the ECM and brought it with me (drove the Altima).
I dropped it off at a UPS store in upstate New York and shipped it to the Medics.
Took my vacation, and then picked it up again at the same UPS store on the way home. Five bucks in shipping each way. Can't do better than that.
I also bought the new IACV in Florida. Cheaper than here.
Put it all together when I got home (in minus 20C weather), started the truck and ran like a charm.
Did the relearn and it's been perfect ever since.
Keep us up to date.
Hope it all works out for you.
Cheers.