2jzgte #2 turbo IACV opens on idle

**Daddio** · 30-01-2013, 03:18 PM

OK...will give it a go...

**Daddio** · 03-02-2013, 11:28 AM

Tried TTc mod...
Bit flat on the bottom end, and virtually nil boost below 3000rpm (as to be expected) made 7psi at 3000rpm, and got to 21psi by 4000 on full throttle (despite EBC being set at 18). Then hit a wall again at 4500rpm (stayed at 20+ psi until it started dying at 4200rpm) Tried again with EBC switched off, still hitting 20+psi and cutting. Tried increasing boost limit on PowerFC to 1.4 bar (20psi + 2psi=22psi) still same.
Could it be the MAP sensor (stock) is running out of range? I have a 3 bar MAP sensor here, will plug that in and configure and see what happens...
I have no idea why the EBC isn't controlling boost...

**PlacentaJuan** · 03-02-2013, 11:37 AM

How is your ebc connected?
Have you bypassed all the wastegate vsv's?

**Daddio** · 03-02-2013, 11:42 AM

I only bypassed the two vsv's shown in the ttc mod thread (inlet air and exhaust gas control valve)

Edit: Sorry, the EBC is plumbed between the pressure outlet and waste gate on the front (no.1) turbo.

**Daddio** · 04-02-2013, 10:50 PM

In case anyone is interested, figured out today that disconnecting the TRAC throtlle plug fixed the issue. I dont know why it was closing (TRAC light never came on) but seems that was the issue. Now to figure out why...

**woggin** · 08-02-2013, 04:14 PM

ha, thats interesting, i know if u go big stall, say 3.5k for example, the trc wont let it get onto it all the way, itll just hold at 2.9k (for eg) dont know wat it is specifically, but the trc system limits the throttle, must be a speed sensor V rpm limitation on the software, glad to hear that its sorted tho!

**BMWTurbo** · 28-04-2013, 10:42 PM

A bit late, but the IACV should open when backing off the accelerator to bleed air off from #1 turbo. The BOV is undersized and iif the IACV didn't do this you'd get the #1 turbo forcing air back into the compressor and the typical large turbo chop of air.

Here's a Video of what it 'should' do. I was using air to feed this though so acts faster than normal.

**Draven** · 03-05-2013, 04:35 PM

Originally Posted by Daddio

In case anyone is interested, figured out today that disconnecting the TRAC throtlle plug fixed the issue. I dont know why it was closing (TRAC light never came on) but seems that was the issue. Now to figure out why...

That's very interesting, because your symptoms almost exactly mirror what i had when the exhaust wheel of turbo #2 decided to take up residence in the cat (except the TTC mod simply resulted in low boost up to 2lrpm before going back to 0psi)

**PlacentaJuan** · 05-05-2013, 06:31 PM

bmx turbo thanks for that i knew it was opening deliberately but could not find ANYWHERE that described it or mentions this.

so how would this affect fitting one of those vacuum switches to the #2 iacv?

some people do it when boosting both turbos so that #2 prespoo0ls to a higher boost before its allowed to join the fun.

im guessing that this signal would be disabled with the vacuum switch

**BMWTurbo** · 07-05-2013, 09:16 PM

Originally Posted by PlacentaJuan

bmx turbo thanks for that i knew it was opening deliberately but could not find ANYWHERE that described it or mentions this.

so how would this affect fitting one of those vacuum switches to the #2 iacv?

some people do it when boosting both turbos so that #2 prespoo0ls to a higher boost before its allowed to join the fun.

im guessing that this signal would be disabled with the vacuum switch

You'll end up with typical 'vl style dose' unfortunately.

I did a write up on using a check valve to limit when the IACV opens. There is a way around this by using a second VSV triggered from the TPS idle switch or the like, but in reality it's a whole lot of effort for not a huge gain.

The factory BOV can also be 'opened up' internally to try and bleed some more air off through the BOV rather than having it chopped back up by the #1 compressor, this helps a bit also. I also mod'd by adding a second spring the BOV, which unfortunately also has a negative effect in that it takes more vacuum to open, which isn't great at light loads.

TBH though with the stock twins a larger exhaust, some more boost on #1 and both and some form of mixture adjustment, with the std twins and a GC VSV/vacuum/boost system I don't feel the IACV check valve mod add's a lot of value. My std twins wouldn't drop boost at changeover when I had the above done. ie 13psi then 18psi on both.

It's when you are going high flows etc that this mod and changing the changeover RPM value that good gains can be noticed.