High Idle Issues

[ido09s]

Morning all

Need some ideas on where to start.....

Had the car on the dyno last night for some further tune work and all was going alright until the car had a small misfire at about 25psi and 8000rpm.

All is fine, the car still runs fine and hasn't had a terminal issue, but it now idles at close to 1600rpm.

First things first, a smoke and pressure test was done on in the intake, no problems. No leaks, holds pressure. Sprayed down all the throttle bodies, though I have since found out it was with water not brake clean, and no change to the idle. Though I will try with brake clean as I believe this would be more effective.

There is no AAC valve on the intake, its plated off, though I am suspect it may have developed a leak between the 2 sides under the plenum causing the issues.

Ata bit of a loss at the moment as to what it could possibly be as the leak appears to be somewhere inside the intake.

I am all ears and I need some ideas on where to start as I really don't want to take the inlet off the damn thing!!!!

[Scott Black]

what was done in this further tune work,
how are you controlling idle without the aac valve,
what model rb is it? assuming its a 26 as you mention multple throttles
what ecu are you using?
if its a 26 how did you spray down all the thottles, and why did you use water for that?

[GH05T]

if its a 26 don't clean the throttles, you will remove the sealing film and this will make a high idle worse.

[ido09s]

what was done in this further tune work,

how are you controlling idle without the aac valve,

what model rb is it? assuming its a 26 as you mention multple throttles

what ecu are you using?

if its a 26 how did you spray down all the thottles, and why did you use water for that?

all it was was a boost controller and a tune. The engine has been in the car for 8 years or more and its always idled fine off the throttle stop screw. Something happened at the top of the last dyno run and now it idles at 1500/1600rpm

Ah yes, sorry, its a 26 with stock inlet side. Its got a Link G4 in it so map sensored and it runs perfectly still once off idle

By spray them down i mean all over the outside of the inlet. You spray it with brake clean, which i did on the weekend, and if there is a leak you will notice a change in the idle. Sorry to day there was no change to the idle so somehow its an internal vacuum leak which i had no idea could actually happen.

GH05T, motors been in there for years. I am totally aware of the seals on the butterflies but its long gone.

[GH05T]

mine also has had some idiot perfectly clean the throttle bodies. with the idle screw all the way down it still idles at 1200.

I fixed that with the haltech but prior, I just could not get the idle comfortably under 1k with the seal gone.

[ido09s]

its idled fine for years. Starts fine on cold start up with large cams and E85, its never been an issue. Its the misfire on the dyno that has done something and its definitely an internal vacuum leak it seems as nothing I do externally fixes the issue.

I had no idea you could even have an internal vacuum leak!!!!

One thing I will do is get a bore scope and check the throttle butterflies, I highly doubt one would be bent but stranger things have happened

[GTSBoy]

Misfire = possible backfire into inlet = bent throttle shaft?

[ido09s]

that's about the only thing I think I can be. Or its blown out the seal around the throttle plate, which was probably non existent anyway given the age of the engine

There is nothing within the inlet manifold it could be is there?

Edited May 16, 2016 by ido09s

[GTSBoy]

If it is not leaking so that you can find it with a smoke test or carby cleaner spray, then the best candidate is the throttles are more open. There is no such thing as an "internal leak"....well except maybe for breathing through the crankcase. Have you had a look at the PCV stuff?

[ido09s]

the guys thought that there was a chance that the AAC area could have generated a leak as part of that would need to be open to atmosphere or the AAC wouldn't work, BUT the actual AAC valve is gone and blanked off so wasn't sure if there was something else in the tank it bolts to that could be causing it?

Would a bent throttle plate show up when you pressure test the inlet system? it held really good pressure as well when it was tested

The PCV valve was removed and plugged up with a grub screw. Straight to a catch can from the rocker covers

its only when it gets hot as well which would indicate something is expanding and causing the leak. I let it idle for a good 10 minutes yesterday and it wouldn't idle high. Took it around the block and got some decent heat into it and up went the idle so whatever it is its going to be a bitch to find as I don't think its going to be very obvious

Edited May 16, 2016 by ido09s

[GTSBoy]

Get it hot then do the leak tests again. Something could be opening up to the world that can't be found when cold.

[ido09s]

it was stinking hot when the initial tests were done. We checked before and after that it still idled high and it was so the leak was there. It was still strapped to the dyno while we did it and it all tested ok which is why I am lost. Short of pulling the inlet off the damn thing I really don't know where to look

I guess that's just what I am going to have to do.

[GTSBoy]

Have you done the simplest things like looked to see if the two halves of the TB set are out of sync/adjustment?

[ido09s]

not yet, only performed the smoke test, pressure test and checked it for external leaks with break clean.

I started this thread more so in case someone had had something similar happen before that had a weird fix to the problem.

[gmchaser]

This happened to me in an rb25. 8000rpm spark cut rev limit is what did it. I didn't figure out what it was but kept hearing a hissing sound when loading around the inlet manifold gasket. Also boost was lower than usual after. Is the car running the same boost pressure as before?

[gmchaser]

I also pulled the inlet off thinking it was the gasket but the gasket look fine. Haven't put it back together yet. Damn rb25 inlet is a pain

[ido09s]

no we didnt run it again but i am pretty sure the boost wouldnt have changed as there is no leak to atmosphere. There is nowhere the boost can be leaking to as the inlet side is as air tight as its going to get

[bigmikespec]

On 17/05/2016 at 2:55 PM, ido09s said:

no we didnt run it again but i am pretty sure the boost wouldnt have changed as there is no leak to atmosphere. There is nowhere the boost can be leaking to as the inlet side is as air tight as its going to get

Brad did this get fixed?

[ido09s]

not yet mate

I have pulled it apart though and I am hoping it may only be the throttle bodies. Looking at them with a torch behind them they are a bit dirty and have a few decent gaps. I cleaned one pair up and they look vastly different, little to no light coming through them, so I am going to put it all back together with cleaned out throttle bodies and hope for the best