V36 250gt hesitates when taking off from stop

[Silin]

V36 250gt hesitates when taking off from stop

Hi everyone first post here and I really need your help!! I'm located in Auckland NZ.

My 2007 v6 250gt (vq25hr engine) hesitates when accelerate from stop with light throttle. Rev goes up to around 1200rpm and suddenly drops to around 900rpm then up again to normal. Car would shake and lose power for a blink of time. It ONLY happens right after the car is warmed up, say after 5 to 10 minutes of driving. No problem at all when engine is cold and the symptom goes away after another 10 minutes drive.

I started noticing the issue after I cleaned throttle body and replaced battery.

So far I have put new battery in, cleaned throttle bodies and MAF sensors, changed air filters to kn. Reset ECU by disconnecting battery and releasing remaining charge by pressing bake pedal. I have also done all the relearn processrues. But none of them made any difference.

There is no CEL or code. 

I have even swapped two throttle bodies and MAF sensors but that didn't help neither.

I am having bad mileage too at 7.2km/l when driving moderately in city.

Any ideas??? I have read so many posts and don't really know if I should have a software update or change the exhaust valve or ???

I'm so frustrated:(

Thanks!!!!

[Silin]

BTW idle is stable at around 750rpm after car is warmed up. About a month ago I changed engine oil 5w-30 and transmission oil.

[30ONA]

Vacuum leak? Check the intake pipes aren't cracked or loose.

[sonicii]

This sounds like something similar to what affects some early V36s where the engine coolant has warmed up, but the oil isn't yet fully warmed.  the VCT is quite sensitive to oil viscosity and doesn't function correctly while the oil is still thicker.  i think there was an ECU update to extend the time after warm up before the VCT starts functioning, but it can be hard to get updates for JDM vehicles once they are outside Japan.

 

Perhaps try a different type of oil..

[Silin]

On 1/2/2017 at 4:50 PM, sonicii said:

This sounds like something similar to what affects some early V36s where the engine coolant has warmed up, but the oil isn't yet fully warmed.  the VCT is quite sensitive to oil viscosity and doesn't function correctly while the oil is still thicker.  i think there was an ECU update to extend the time after warm up before the VCT starts functioning, but it can be hard to get updates for JDM vehicles once they are outside Japan.

 

Perhaps try a different type of oil..

Hi Somicii, thanks for the reply! Yes I suspect it's the VTC as well.  I have opened the VTC cover to remove any jam or gum but it turned out all clean. I'm currently using 5w-30 and will change to 0w-40 which is thinner in next service. I'll post back how it goes with different oil.

cheers! 

[Silin]

On 1/1/2017 at 9:07 PM, 30ONA said:

Vacuum leak? Check the intake pipes aren't cracked or loose.

Hi mate I have checked all pipes there's no sign of leak plus idle is stable and once car is fully warmed up symptom goes away immediately.