TwinTurbo.NET: Nissan 300ZX forum - I understand all the routing - just not what I was ...
People Seeking Info

Subject I understand all the routing - just not what I was ...
Posted by 300NASeattle on July 04, 2018 at 7:46 PM
  This message has been viewed 195 times.
In Reply To Link below shows a visual representation. On the drivers posted by jzack on July 04, 2018 at 04:17 PM
Message experiencing during the water and Seafoam cleaning.

I did figure the vacuum difference issue between left and right throttle bodies. I did another vacuum test by using a compressor and getting the intake to 5 PSI and found that I had put the passenger side electrical gallery rear bracket between the balance tube and the plenum - instead of on top. Doh!

The car drives even better than my first test drive after the plenum install. The idle stays lower at 1500 whens it firsts starts cold and drops to 1100 in 5 to 10 seconds. So there is that improvement :).

I still have some type of air leak somewhere that does not show up when I pressurize the plenum though. The AAC valve is mostly at 12% and I can not reduce the idle during the base idle active test (Conzult) below 730 RPMs. I can back out the idle screw 3 or 4 turns from all the way in and then I will get an increase in RPMs.

All the things I have checked,

* Checked the throttle body butterflies and saw that they are both nice and tight. The passenger one shows the entire vacuum hole while the drivers side has the butterfly covering 1/3 of the hole diameter. They are both at the same angle and both appear to be in perfect sync. I also tested with strips of paper and they both close tight enough that I can not pull the 20 LB paper out when they are fully closed. I can also pull off the intake pipes and it doesn't affect the idle. There is no air leaking passed these butterflies.
* Every plenum hose is new. I checked everyone for leaks by misting water, pressurizing the plenum, and blocking them off one by one. They are not leaking there.
* I double checked that there were no leaks around the fuel rail isolators and plenum gasket. No air leaks.
* I closed off the incoming hose to the air regulator and it did not make a difference in idle. I could feel a vacuum slowly build when I had my thumb over the pipe but there was no real air volume.

The last one has me stumped.
I removed the hose going into the IAA unit and plugged the metal tube and the idle finally dropped to 550 - 600 RPMs. The only air getting into the intake is either from air leaking by the throttle body butterflies or some other air leak. Do you think that the engine should stall when you plug the IAA unit incoming air?

Seems like it should to me.

The car does run great and there is no hesitation and it idles nicely but this idle leak is still eating at me. I want the AAC valve to be within the expected 20 to 30% at idle. I also saw that when I was doing a test drive and I had my laptop hooked up to the car with the Conzult cable that the AAC valve was at 55 to 70% - I would think that it would be at 0% or at least very low during highway cruising speeds since the air coming through the throttle bodies.

Driver's Side Throttle Body

Passenger's Side Throttle Body

AAC and Speed graphed

RPM and Injector Duty Cycle graphed

Follow Ups  
Post a

You cannot reply to this message because you are not logged in.