Rb26 Dies/stalls After Letting Off Gas. (video)

[xripstickx]

I have been struggling with this issue for a long time now and I cant seem to get it sorted out. When i let off gas the engine either dies or comes very close to it. While driving if i let off the gas to prepare for a turn the engine RPM drops so low that it looses oil pressure and power steering stops working for a few seconds until the engine recovers and bounces up to a good idle. Also can not get any good pull out of it because when i clutch to change gears the engine wants to die.

I have capped the turbo inlets and charged the system up to about 20 psi. I found a few minor leaks and patched them up. I also isolated and capped anything that is not necessary. I removed the BOV's and capped it. Plugged the vacuum, line that actuates the BOVs. disconnected the PCV and capped both lines. I also capped the line going to the charcoal canister.

I can not figure out why this is still happening!!?! Any ideas?

While trying to correct this issue over more than a year now I have:
Replaced the plugs
Replaced the coil packs with splitfires
Ordered new blitz BOV's (not usuing BOVs currently)
Replaced both MAFs
Installed greddy intercooler piping
Replaced all post compressor worm style clamps with t-bolt hose clamps.
ALL of the equipment I mentioned was NEW

I also have an APEXI Power FC ecu but havent yet got a tune. Whether im using the stock ECU or the Apexi running a base map, it doesn't change the issue either.

I am Stumped guys. Hopefully someone has an idea of whats going on!!

VIDEO BELOW (not sure how to embed so i tried a few ways)

<iframe width="560" height="315" src="https://www.youtube.com/embed/y_4PPMdgUYk"frameborder="0" allowfullscreen></iframe>

[xripstickx]

Also ECU self diagnostic is throwing code 34 Knock Sensor

[baicai]

Seen this happen on an r34 gt-t, rev engine and when the revs come down engine would die. The engine idle was still set at 500-600rpm and would drop below that so engine kept dying. After adjusting idle control to 900-1000rpm it fixed the problem. Not sure if it is the same in your case but worth a try.

[Dose Pipe Sutututu]

Install stock bovs, install bov returns back to the intake.. oh wow everything is normal again.

I suggest you refund those bovs and spend that money on blow and hookers.

[xripstickx]

I have the stock recirc valves too. I tried that. Still the same issue.

the idle speed is good the problem is only after acceleration when returning to idle it stalls.

I am looking into this knock sensor issue and I am noticing that i get a .5 Mohm on the ecu harness knock sensor 2 and unlimited on sensor 1. I am not sure what one is 1 and 2 on the block though.

Also not sure if this is related to the issue but i have read that a disconnected knock could put engine in a limp mode.

[Trex]

but you can put resistors inplace of the sensors. i wouldn't suggest it, but was used a lot 10+yrs ago if you want to search for the threads.

[xripstickx]

so just a 500k ohm resistor from the knock sensor 1 pin on ecu harness to ground? At least to see if this is whats causing my problems?

Can i just put a jumper off of the pin that has the working knock ? or will this throw off the resistance for both?

Edited April 3, 2016 by xripstickx

[Sinista32]

TPS

IACV

Earthing

Throttle body

[Sinista32]

^ Just a few extra things to check

[xripstickx]

Update, I got the ecu throwing 55 now but the problem has not changed. Also the problem seems to be much worse once the engine hits operating temperature. While its cold it seems fine.

Now im looking up exactly how to test the things sinista32 listed.

[Sinista32]

Add water temperature sensor. Not the one at the radiator.

[GTSBoy]

Pain in the arse suggestion, but try dismantling and thoroughly cleaning the idle control valve. Once that is done, then see about setting the throttle stop to a slightly larger opening.

The thinking behind the above is this.....IAC is sticky/slow so someone sets the idle speed by fiddling with the throttle stop position. The throttles now sit a little too closed. When you rev it they slam shut and the revs dies pretty bad and 25% of the time the IAC is not fast enough to catch it and the other 75% of the time it does catch it but it sucks.

[xripstickx]

Pain in the arse suggestion, but try dismantling and thoroughly cleaning the idle control valve. Once that is done, then see about setting the throttle stop to a slightly larger opening.

The thinking behind the above is this.....IAC is sticky/slow so someone sets the idle speed by fiddling with the throttle stop position. The throttles now sit a little too closed. When you rev it they slam shut and the revs dies pretty bad and 25% of the time the IAC is not fast enough to catch it and the other 75% of the time it does catch it but it sucks.

Do you think I could just block the air supply to the IACV and the AACV, then adjust idle with throttlestop and see how it responds? Looks like ill need to take the intake manifold off to get at the IACV and i dont have an extra manifold gasket at the moment.

My thinking is if someone did adjust the stop for a sticky IACV I can just block it completely and adjust the throttlestop to a position that will keep it stable and not have to factor for the extra air coming from the sticking IACV. If this works that would point to a dirty/sticky valve. Im all about trying to eliminate possibilities as easily as possible so I can identify the problem before i spend more time fixing stuff thats not broken.

I am thinking this is a good troubleshooting step but im sure most people on here know more about rb26 than I do.

[GTSBoy]

As a troubleshooting step it will work. It will not be a good solution because you won't have idle control - you'll only have whatever flows past the throttle plates.

[xripstickx]

As a troubleshooting step it will work. It will not be a good solution because you won't have idle control - you'll only have whatever flows past the throttle plates.

i found this description on another forum.

"gtr.co.uk"

IACV (Idle control valve)

I'm not overly knowledgeable about this component as I don't actually have this on my car. A lot of people remove this and/or block the piping and rely on tuning to do its job. It is located very much under the air plenum above the oil filter.

Basically, this component will allow more air into the system depending upon how cold the water temperature is. As the water temperature rises, the valve will gradually shut until this device is no longer used.

if this description is correct wouldn't it not matter if i blocked it off completely?

edit: after more research it seems this is not actually how it operates at all. can anyone confirm?

Edited April 4, 2016 by xripstickx

[xripstickx]

seems like if IACV was sticking and not responding to the quick release of throttle fast enough then you could expect it to act like its starving for air momentairly until it catches up!

Going to go forward with that. Ill remove it and clean it and let ya know how it goes.

Anyone remove this without removing the plenum?

[GTSBoy]

Yeah, FYI, these old Nissans have 2 valve. The water temperature controlled one is the cold start valve. It dumps a lot of extra air in when dead cold to get the idle speed right up. Pretty much any time the engine is running warm that one should be closed and out of play. The other valve is the actual idle control valve. Its variable opening is controlled by the ECU.

Later cars have the two functions integrated into a single unit. On 25Neos, for example, it is in the same location on the back end of the plenum as the IACV on older RB25s, but it also has the wax pellet water controlled bit in it as a separate air path.

The location of these valves on an RB26 is why I started my first post with "Pain in the arse suggestion".

[xripstickx]

That makes perfect sense as to why it doesn't seem to have this problem when the engine is cold since the second valve is wide open allowing the engine to breath through that while the IACV is slacking.

It might be a pain in the ass but so is me trying to figure this out for the past year with no help. I feel pretty optimistic about it and cant wait to get to working on it tomorrow.

Thank for the help!

[xripstickx]

Anyone know a good write up on removing/cleaning the IACV?

[GTSBoy]

Not off the top of my head, but if you were to search these forums (use google and point it to sau.com.au) then you WILL find one.

But it's basically just a case of lots of carby cleaner, some dismantlery and pocking with pipe cleaners and shit.