ssaskee

Hi,

I have Nissan 350z 2007 with VQ35HR engine. I had a problem with surging idle between 1800-1500. I don't have any mods except cat converters were removed by previous owner and it is just straight pipe instead of them.
I took car to several mechanic shops where it has been checked for leaks and apparently there are no leaks (test was done with smoke). We found online that it could be ECU issue, and I bought Uprev software and we re-flashed vehicle on
suggested ROM, no changes. MAF sensors were cleaned, throttle bodies are clean, we tried to disconnect all kind of sensors and there was no change in RPM's. Then I replaced PCV valve and the car stopped surging from 1800-1500 but still has
really high idle but just bellow 1800 so it doesn't surge anymore but constantly running high. The only thing helps is when to try to re-learn it with "Nisscan |||", but this action never complete successfully, but in process of doing it it still lowers RPM to a little above 1000.

Problems:

If the car is on low RPM while driving (bellow 2000) it is jumpy it shakes when u want to accelerate or even when you decelerate and it comes to this RPM area.
While driving over 2000 RPM the car drives perfectly, accelerate normal, not sluggish at all, everything seems perfect.

This is after relearn so the RPMs on idle can even come down to a little above 1000:

If I want to accelerate really slow and constantly on idle from 1000-3000 at first there wont be any effect, then after a while when RPMs should be around 2000 the car starts building up RPM really fast and around 2500 (I'm still pressing the accelerator pedal constantly on same spot or really slowly a bit more) the RPMs drop to approx 1500 and the they go back up and accelerate as it should.

If I press pedal strong and RPMs go up to lets say 3000-3500 they will drop smoothly until 1500 and then they will be dropping really slow.

I did several data logs with Uprev software but they stopped replying my emails so I'm really lost and If someone has any idea how can I get till the bottom of this I would really be gratefull.

I will attach logs, and chart of slowly acceleration on idle, if someone maybe knows what could be my problem.

Thank you very much guys and if you need any other input please let me know!

Best regards


Both pictures of charts are from same log where I try to slowly and constantly accelerate from 1000-3000:

This is ignition timing vs RPM.


This is after relearn logs of both accelerator positions which I can get from logs, both maf sensors, both throttle bodies vs RPM.

seymore4

iTrader: (27)

What rom did you use with Uprev? If you used another 07 file that's not going to fix anything. You need to flash it to the compatible 08 rom, then do the relearns.

icer5160

iTrader: (4)

Do you have a Check Engine Light on? Have you scanned for any active DTCs? With this type of behavior, there's normally some indicator that there's a problem and that could help troubleshoot/diagnose.

It could be related to the throttle pedal position, cam sensors, crank sensor, maf sensors, cam magnet retarders (VTC system). Throttle position sensor, intake manifold vacuum leak.....many many things.

What is clear, is that your computer is not getting good data from one or multiple sensors.

Things I would check in live data:
Fuel Trims (AFR), O2 Sensor (upstream), Throttle position sensors, timing advance/retard.

See if both banks have similar or matching data. If a sensor seems lazy/slow that could also cause odd behavior.

Good Luck!
-Icer

ssaskee

We tried EV16A, EV16B which are 2007 roms and EV21A which is suppose to be 2008 rom, with all it was unsucessfull

Thank you for your response!

ssaskee

There is no engine/cell light, yes it was scanned for dtc but there are none :/ The upper charts/logs have MAF, Accelerator and throttle sensors compared to RPM so you can see their data.
There is also ignition timing vs RPM on second chart but I dont know how this data should look I'm not expert.
The car was checked with smoke tests and there is no vacuum leaks.
In data logs there is long fuel trim which also looks good (but again I'm not expert), but cannot log short fuel trim with uprev app, will try to make logs with another app also of short fuel trims, and post them here.

I will try with cam and crank and vtc system replacement.

Thank you both for your responses!