Sorry if I have missed a existing thread about this, but I didn't see anything that quite match what's going on, so I figured I'd ask everyone here..
I have an 01 Maxima GLE Auto w/Trac Control. The car had an P0505 code when I got it, ran fine other than a slightly high idle 1000-1100, and a slight idle dip when first started when it was cold.
After about a week while I was waiting for my IACV to arrive, it got to the point of where it would set itself to high idle like 2000 rpm and not come down. I replaced my IACV and attempted a relearn process using Nissan DataScan II. It would only tell me ECU Busy and count endlessly. Once warm the car started surging the idle from 1500-1750 over and over. I noticed that the IACV driver in the ECU was cracked in half almost.
I ordered an ECU that claimed it was refurbished, but it seems that they only listed it that way, as at one point Nissan stamped it refurbished. With that ECU the Idle was still high, but it wasn't bucking. I looked in that ECU and there was heavy corrosion on the back of the IACV driver solder points, so I sent it back under the assumption it was dying.
I sent the ECU out for repair, they said that they replaced the driver and it passed all tests.
I also then disconnected the electronic motor mounts per the instructions.
I reinstalled the ECU and noticed that the TPS was out of adjustment. I replaced it with a new TPS and set it correctly. With the TPS set correctly, and adjusting the idle screw to bring the idle down, I was able to get it to pass the idle learn in the Nissan DataScan II software. The issue that I am having though is that the surging occurs when the car is warm and the ECU sees that the throttle is open. Once the throttle gets pressed a fair ways down then it stops the bucking and revs up quickly. The second it sees it's open the surging starts, be it when the throttle is actually opened. Or if the TPS is rotated in correctly and the car just thinks its open. The ECU is jumping the timing all over the place when it's doing this idle surge also.
I tested the resistance with on the old IACV motor and it passed the test. I tried the old IACV but the issues are present with it also.
I used a smoke machine and didn't see any vacuum leaks, but I will double check that later.
What I'm wondering though is, does it seem likely that the other ECU wasn't truely defective, just that that the TPS and idle screw was out of wack. And now that I have my "repaired" ECU back, that it has issues other than just the driver chip, which is causing the surging in RPM? Or is there something else that I am missing to check which commonly causes this?
I had the same problem with mine there is no real info I say this because it took me nearly three years to sort it. I smoke tested engine found nothing but used soap and water and found leak in intake gaskets throttle body gasket and several hoses all very small leaks. also throttle body was dirty needed cleaning I actually steeped in white spirit worked a treat and my MAF was toast as well as was my bank 2 sensor 1 o2. and injector on cylinder 3 and ignition coil on cylinder 5.my IACV and thermostats were also kaput stopped the surging. but because it took so long to fix it killed my two precat's. I do think the surging idle was down to intake gasket leaks though.
have the exact same issue, one day it started out of the blue, park/neutral/1st gear only 1600-1800rpms range only
replaced:
4x o2 sensors
MAF
IACV
TPS
throttle body
Nissan factory reman ECU (motor mount connectors not plugged in) (original ECU did burn)
i've tested a bunch of stuff from Haynes and everything is in spec
nothing helped! the thing is the issue occurs only in closed-loop with 5-10% throttle/no load
open-loop runs perfect, anything more than 10% throttle input, perfect, going uphill, perfect, 2nd+ gear, perfect, below 1600 & above 1800rpm perfect
i've read 100+ threads/videos of people having exact same issue and no solutions, "maybe try this" i've tried them all and zero improvement
well... after 6 months of suffering replacing all kinds of parts, i was beginning to lose patience and was about to scrap the car
decided to try one more thing, engine running, warmed up, start unplugging sh*t under the hood ! one by one, every single connector, unclick
sometimes the engine would die ... uhh... better plug that one back in... click so after a few hours at this i located the problem
Thank God
turns out it has something to do with the wiring from the grey connector of the TPS to the ECU, now i previously either disconnected the red one or both and that solved nothing
then somehow i got the idea to unplug only the grey one and problem solved, I could not believe it
I went through 3 TPSs and i checked all the signals from them with a multimeter and everything was in spec
my guess is when i got the P0505 fried IACV and fried ECU issue it must have fried these wires too?
anyway the TPS is sending the signal to the ECU but the signal it receives is bad and then it can't figure out wth is going on and cuts off the fuel
from there is the jerking / bucking / rpm wandering / erratic shifting, you name it, all gone now.
makes sense why i could not find a solution anywhere and no mecanic could figure it out, that's some ghetto "diagnostic" work right there
I suppose a real fix would be to now rip out the entire wiring harness and find the short, then repair it but, oh no, I ain't doing any of that.
car runs perfect now and i'm just going to leave it like that.
note that prior to this "fix" the transmission would shift poorly at times and the car would jerk around when decelerating anywhere in the 2500 down to 1500 range
now all of that is gone, you cannot even tell what gear it's in, both up and down shifts are very smooth
in case you're wondering that that liquid is on the black hose, it's blood
