Recirc. valve/MAF relationship

[bobbo]

I have a high idle problem I'm trouble shooting. ALL of the usual (and unusual problems have been elimated. There are NO vacuum leaks and everything is functioning normal.
Where I'm at now is...
I have the recirc system disconnected on the filter side.
If I plug where it goes into the intake side AFTER the MAF the idle drops to normal.
I'm trying to determine if the recirc system is functioning properly.
I'm running a PFC and suspecting I may have to play with the MAFs to solve the problem.
Also, when the engine is at idle should the recirc valves be open or closed?
Thanks for any input!

[archaeic_bloke]

should be closed at idle, they only open AFTER building boost and letting off throttle, and even then they are only open momentarily.

leave the recirc system all connected the way it is, thats the best setup for response.

you can tell if the valves (BOV) are stuck closed and not working if you drive the car, build boost, and letting off the throttle you hear turbo flutter/comp. surge.

[Skym]

With Synapse BOV (pull type) the valve is open at idle and closes as engine transistions to boost, as shown in this videoclip -

http://www.youtube.com/watch?v=MU5Y6d9rh1k

Stock BOV (push type) would have vacuum (engine sucking air into intake manifold) hose to top of BOV, so might be slightly open at idle. When engine transistions to boost the valve is held closed by boost through vacuum hose to top of BOV. But from what I have noticed, the spring is quite hard and takes a bit of force to open valve, so most likely it's closed at idle unless vacuum of engine is very strong. What you could do is simulate the vaccum with a hand pump, gauge (to match engine vacuum which should be mentioned in a engine manual) and see if it opens.

A known problem is the valve can leak around the edges (had to replace stock BOV with another because of this problem), so remove BOV and clean surface of flange and around valve. Then blow on valve to see if you can feel air (on the recirc side of BOV) getting around valve. Another cause of airleak that I found is BOV flange gasket, which is use once only. So would need to replace BOV flange gasket everytime you remove BOV. Once the ridge in middle is crushed, BOV gasket doesn't seal after refitting BOV. Same gasket as used on exhaust manifold to turbo flange on GTS engine (might be the same on GTR, but never looked).

If you block the little hole next to main valve on bottom of stock BOV it doesn't quick release at lower boost levels and if it does open at slightly higher boost levels, a flutter sound can be heard from podfilter. When travelling up a hill and back off throttle, the BOV opens properly (loud sound). The little hole helps BOV to properly open (quick release) at lower boost levels. But if blocked it helps BOV to not leak after 10psi for GTS (I think GTR BOV's have a harder spring).

Recirculating BOV is due to placement of MAF's (infront of turbo's). If you remove air behind MAF's via to atmosphere BOV's, ECU has no way to know that it's been removed and inject's fuel to match what MAF sees and engine stumbles or stalls due to running too rich. If use a ECU with MAP sensor it measures the amount of air at intake manfold, so ECU can compensate.

Can run a Synapse BOV with antistall fitting if you want to run to atmosphere with MAF's -

http://www.youtube.com/watch?v=zZ71gaubqS0

[bobbo]

Thanks guys. To add to the question I've discovered this...
With the system assembled the car idles smooth at about 1600 rpm.
If I remove the intake manifold charge pipe the idle drops to a smooth approximate 1000 rpm.
Any thoughts to what might be going on here?
Thanks!

[Skym]

Is the idle valve rpm vs ECU idle rpm (factory is around 950rpm for RB26 according to stock idle rpm table) set correctly (both at same idle rpm)?? If idle valve is set higher, idle rpm sits higher. Also IACV can cause high idle if not closed fully (could stick due to oil deposits from blown turbo or blowby gas). Some on GTRC have had the IACV problem.

[Black BNR32]

it won't matter if the valves are leaking

your mafs will see the same amount of air at idle regardless (assuming no leaks)

I have the recirc system disconnected on the filter side.
If I plug where it goes into the intake side AFTER the MAF the idle drops to normal.

this makes me suspect a leak between the recirc valves and the intake connection you plugged

If I remove the intake manifold charge pipe the idle drops to a smooth approximate 1000 rpm.

but, this makes me suspect the idle air control valve. i'm surprised the car runs like this as your mafs won't be seeing any air. you could try cleaning the idle air control valve as they can stick

and, make sure your maf sensors are clean.

how are you testing for leaks?

[bobbo]

I have a brand new IACV, all new vacuum lines, I pressure tested the system between the charge pipe at the turbo exit and the hose going to the I/M and that's tight.
The AAC valve has been completely cleaned, reassembled, and checked for air leaks.
One thing I did find was the coolant vent at the top of the engine was plugged. Might have had an air lock. Fixed that.

Is the idle valve rpm vs ECU idle rpm (factory is around 950rpm for RB26 according to stock idle rpm table) set correctly (both at same idle rpm)?? If idle valve is set higher, idle rpm sits higher.

Sorry Skym. What is this "idle valve" of which you speak?

[Skym]

AAC valve has to be calibrated to be at same rpm as what's set on ECU. Basically AAC valve 950rpm, ECU 950rpm. If not calibrated, idle rpm might be a bit higher.

Another cause could be misadjusted TPS (but you probably have already adjusted this).

[bobbo]

Sorry I omitted a critical point. I'm now running a PFC. I've done the idle self learn but since then I've changed vac lines among other things.
I've now got the idle from about 1650 down to 1100. Sadly where I did and changed so many lines and put the new IACV in I have no ideal what made the improvement.
I did verify the TPS value with the PFC and it's at .48V-.49V.

Thanks Skym!

[Skym]

Not sure how I helped, but you're welcome.

[bobbo]

Not sure how I helped, but you're welcome.

Your helping and that's.... something special