On a 1988 S4 is there any kind of internal check valve or other opening/orifice that could allow air to be sucked into the intake or combustion chamber that shouldn't be.
I'm still fighting a high idle and the usual, and even some unusual, suspects have been looked at ad nasuem.
I'm looking for something really weird...something just shy of ghosts or screen doors to the fourth dimension inside my engine!

 

is there a chance that the intake rubber inlet has a crack that you have not found?? with a blower there are problems with the rubber portion cracking possibly next to a clamp

 

I wish it were so, and a lot of symptoms at times point to something like that the way situating the outlet of the intercooler and the MAF boot together can cause severe bucking if it isn't pushed in there just right...not too far...not to short. Apparantly it creates turbulance in the air stream entering the MAF sensor.
The way it acts when that is going on you would think there must be a hole that is opening and closing letting gulps of false air enter into the mix.
I have finally found the spot that almost completely eliminates any sign of this symptom and have it marked on the intercooler outlet and marked the firewall with a reference point so I can get the MAF boot lined up consistantly. Combine that with a consistant method for strapping the MAF sensor to the intake legs and I think the high idle is my only problem now.

The "intake rubber" you speak of I'm guessing is the rubber part under the MAF sensor and I've taken it off at least 20 times and inspected it, tugging and pulling at it warm and cold trying to find the mystery leak...no luck though.
I've tried numerous clamps on it, tried different positions getting the bead of it to sit further up the neck of the throttle body or right in the groove, etc. no leak found.

The last time I pulled the intake I cut some blank steel plates and mated some gasket material to them to block off the intake outlets and plugged the injector holes. Assembled the rest of the components: MAF, intake rubber, ISV with hoses, throttle body, etc.
Plugged all the vacuum and and other ports and pressurized the assembly up to at least 15 psi. No leaks anywhere except at both flappy bearings, top one sealed with zip tie around it's rubber cap, and at the throttle plate shaft where it protrudes from the throttle body to link up to the throttle cable linkage.
At those three points some air will escape. I don't know how much is acceptable...I have doubts that what I saw is enough to give me the extra 300 rpm's. Then again I'm a rookie so maybe that is it.
I have Roger sending me some different flappy bearings so there will be a double seal on them but the throttle linkage will still be a wild card.

Here's a test for you SuperShark guys out there: At idle, engine warm, pinch the rubber hose between the blower outlet and the intercooler inlet with both hands, fingers under the hose thumbs up on top. slowly cause the hose to be pinched off in one straight crimp. How far do you have to go to start lowering the idle speed of your car? On mine it is probably 90% closed off before the idle changes at all...
I don't know if this tells me anything but I'd sure like to know if any other stage3 guys get the same or remarkably different results. my thinking there is if your idle changes much sooner then I probably do have false air keeping my idle up when the hose crimps...or if yours can be crimped almost completely before the idle drops like mine can then maybe my problem is electrical.

As usual many thanks for those playing along! Any ideas will be most welcomed.
I promise I'm ten times more tired of this situation than you guys are of reading about it!

Some stuff I've done/tried:
refurbished my MAF, loaner MAF, refurbished my LH, loaner LH, loaner EZK, new fuel pressure regulator, new fuel pump and filter, removed and cleaned CE panel checked for loose connections, dremel tool with brush to clean all ground point contacts and most of CE panel connections, SharkTuner won't correct the idle speed, the closed loop just compensates for any change I make thus the problem is beyond it's scope (I guess), new vacuum lines and rubber, pressurized intake numerous times and ways, starting fluid as leak check, new TPS, new ISV,.
Probably lots of stuff I've forgotton too.

 

How about installing a new set of flappy bearings with the double sided seal, Roger has them. Also consider inspecting the throttle plate shaft , this can also leak

 

I have a request in to Roger for the bearings already. How do you stop the leak at the throttle plate shaft?

 

86 S/C Murf kit
I'm not sure if this is the same issue as I had but chased it for a long time. Surging bad A/F ratio and erratic idle. May be worth reading these posts.

https://rennlist.com/forums/928-foru...tion-pixx.html

 

throttle shaft needs to be taken apart and inspected.
Look for other things (easier things) first

 

Tank vent system?

 

Craig,

I think I posted in one of your threads about the leak I discovered in my vent system.

From my intake refurb, I had the incorrect vacuum line connected to the vacuum pod that opens and closes to vent the charcoal cannister. Therefore it was open at idle passing false air.

2nd, I discovered that my blow off valve (included in the kit) would not hold vacuum and was not functioning correctly. So you might just check that valve. If should hold a vacuum. I also noticed that now at idle with vacuum on the blow down valve it by-passes (releases) quite a bit of air at idle from the blower.

After correcting these 2 items, now instead of pulling 16 on the vac. guage at idle I am at 19.5 - 20 and a much more stable nice idle.

I will give my tube a pinch tomorrow morning and let you know what I find.

 

Craig,

Sorry for the delayed response, but today I pinched my intake hose as you described in your eariler post.

My idle was not lowered until the hose was almost pinched closed as you describe.

Any improvements as of lately?

 

Right now I have received the new flappy bearings and am just trying to decide whether or not to pull the intake to install them and take apart the throttle shaft while it's out to rebuild it...or....refurbish my original intake including a cleaning and repaint, install the new design bearings in it etc. so I could just pull the intake that is on the engine now and install the original refurbished one all in one afternoon. Since I have spare throttle body and intake manifold I'll probably do the swap to reduce down time.

It's hard to take the car off the road right now even for a day because other than the high idle it is really running well!

 

It's hard for me to believe that what ever leakage you are having thru the flappy bearings is causing your idle to increase 100 - 200 rpm. ( I know some folks here will disagree with me) AND you have the rubber cover tie wraped tight as well.

Today, I also pulled a vacuum line off my front damper causing a fairly good size leak (the size of the vacumm tube) and even though my idle was affected, it did not increase that much. I don't know if this test is valid, maybe the leak needs to be over a longer period of time...

Another thought...at idle, my blow off valve vents a hugh amount of air. Therefore, the blower is pushing much more air at idle that the engine needs and building up pressure in the intake which the ISV also sees at idle. If your blow off valve is not venting correctly could this be forcing more air pressure into the intake causing a higher that normal idle? I think that the more vacuum present at the vacuum port on the valve the more it opens and more air is released. You might just check that.

Anyway, I would place my bet (even thought I did replace my bearings and I am sure it can't hurt the problem) that it will not fix the high idle.

Certian days, especially when the engine is hotter, mine idles a little high as well. And probably I would say my idle averages about 100 rpm higher than it did before the SC. I wonder if the slightly higher idle is SC related on some cars.

Other wise, my car is also running so well, and such a blast to drive I don't even want to put it on jack stands to change out my CV joint boots in the rear. The temp. here today was 78 degrees, great driving weather

 

I agree. Intake leak through the flappy has a very low probability of being solely responsible for an extra 100 - 200 idle rpm. I say low, only because I'm sure that we could think of way to make the flappy components leak more.