One more thing, double-check the torque on your IM bolts. When running the IM spacers, you’ve got two sets of gaskets to compress, and once they seat after a few heat cycles, the IM can be a bit loose. I must go through the torque sequence at least 5 times when re-installing the manifold.
Also, clean up that hose routing! 
Koolade:
Which hose on the intake boot is for the PCV check valve? The one with the clip or the other?
I have the check valve under the IM going to a T to feed the airbox flap solenoid and vac reservoir. Is that correct? The vac lines up front are holding vacuum perfectly.
It’s a braided hose that is a press fit (by hand) into the rubber intake boot. It does have a connector that looks kinda like a 4-leaf clover (for lack of a good term). I just pull the whole thing out of the boot.
Found a pic:
Look to the upper left of the pic and you’ll see the connector for it, and where it feeds down into the valley.
[quote=“komseh,post:42,topic:7650”]
As long as the check valve is the first thing after the vac nipple on the IM, and it’s in proper orientation (holding vac to the systems behind it) then you can rule that out…unless it’s clogged, but I haven’t seen that before. Run the airbox flap test via vagcom and you’ll prove out that part quickly (if you haven’t already). If the vac reservoir has enough to actuate the airbox flap a few times, then that part of the system should be fine.
FYI, The nipple at the bottom of the IM extends ~1/2" into the IM, so that any loose oil that pools at the bottom of the IM won’t get sucked into that vac line.
Funny thing just happened when I drove the car during the high-rpm cold engine start… The car got really bucky under light throttle, complete with a few backfires. It was fine as soon as the idle settled.
Replaced the breather hose o-rings with #13 size from home depot. They are a tiny bit thicker and have a slightly tighter inner diameter than the OEM ones. The passenger side breather hose is still seated with a small gap, but this isn’t the issue anyway.
http://i.imgur.com/Cwmh783.jpg
PCV check valve flows well. I can blow air through it but can not suck air through it.
koolade thanks for the tip on tightening the IM bolts. The middle bolts both took a few Nm, others took 1 or less.
The vac lines up front hold vacuum very well. I left the car sitting overnight and unplugged one of the lines the next morning and it let out a lot of air.
I’ve pretty much exhausted the possibilities of a vacuum leak. I think I will remove the IM one more time and do some tests on the check valve underneath. After that I think I will be close to 100% sure that there isn’t a vacuum leak.
Edit: The fact that the front vacuum lines are holding vacuum should rule out the possibility of the IM check valve malfunctioning, right?
What else can I check that would be causing idle fluctuation?
I’m still suspicious of the driver side SAI pipe that I pried back. It seems unlikely, but it may have separated from the block. If that were the case it would cause an exhaust leak, correct?
karma for koolade great work on the forum today.
Komseh it sounds like your really getting down to the last parts. The vac system has lots of entry points. If you can eliminate as many of them as you can but as you posted dont have a endless journey on it. as there can be other possibilitys
If you can hold vac, your check valve is just fine. Same with the PCV…if the ball can move around without much effort, then you’re good there too.
As for other things:
-Throttle body adaption (there’s a procedure documented somewhere)…Can someone confirm the TB controls our idle entirely and we don’t have an additional IAC in the TB?
-Purge valve leaking/failing (I think this would throw a code though)
-Your exhaust valves are connected (or plugged) properly?
-Do you have a K&N air filter that you over-oiled perhaps? Ever take any MAF readings while the idle is fluctuating?
[quote=“komseh,post:46,topic:7650”]
Yup, that could do it too…
Thanks! And you’re right…troubleshooting can feel like a futile effort at times, but the goal is to systematically eliminate variables until you find the culprit.
What’s the best way to tell if exhaust is leaking from the SAI port on the back of the motor? I was thinking of tossing some chalk around that area to see if it puffs out or something.
koolade, do you recall what size triple square bolts were on the SAI port?
Can you really quickly explain what the car is doing at this point. Stuff like different behavior due to temps or length of the car running would be helpful.
Hrmm, could air pockets in the coolant system put a strain on the system and cause a rough idle?
Thats actually a lot of great information. Normally when you unplug the maf it will help smooth out the idle if there are issues with a vac leak. The fact that the car is doing this when its warmed up is pointing things in a different direction as well. The AC effecting the idle also is important.
Try a throttle body adaption. Unplug the battery and let the negitive and positive cables touch for 45 seconds while they are not connected to the battery. That will drain the system and put the car into a situation where the car will fully relearn the throttle body. Plug back in the battery and turn the key forward but dont actually start the car for 2 min. Then start the car.
This isnt probably going to solve the situation but we will at least know we have a good throttle adaption. We can then start clicking down the list of other things to look at. The bucking and back fireing on cold part throttle also might have a part in this. Check to see that your intake manifold flaps are working properly as well
TBA was done a few times last night. No luck, I was really hoping it would magically fix it :). I will try it again while the car is cold just for kicks.
IM flaps were removed.
I’m going to do some logging of channels 1, 2, 4, 20, 21, 31, 34 during warmup today. Any other channels I should include?
I logged blocks 1 and 2 - fuel correction and MAF readings during the idle fluctuation:
fuel: https://drive.google.com/file/d/0B77pSnYHr8EEekJEY243ZjNnVzg/view?usp=sharing
maf: https://drive.google.com/file/d/0B77pSnYHr8EEQURwdkJyVm84Qm8/view?usp=sharing
The TBA wasnt going to really fix as it was just so we knew the car and the throttle body was ok. The car is raises the idle and you can see that maybe check the throttle and see if that is moving around as well. The log shows us what your talking about but dosent seem to have shown anything major that i can see.
I concur, the TBA was more of a test to see if it was flakey and force it to throw a code if indeed that was the problem. There’s a little dip in fueling that corresponds with the idle fluctuation, but it’s a chicken/egg scenario in that it’s tough to determine if it’s airflow related (ecu responds with lower fueling) or if something is telling the ecu to cut fuel slightly, and that’s what’s causing the idle dip… But like Justin said, there wasn’t anything glaringly obvious.
Allow me to switch tactics a bit…how does it run/perform at higher RPM? Could you run a log (or two) with MAF, throttle position, timing retard, & injector pulse width? Perhaps we can spot a more prominent problem if we force the issue a bit…make sense?
When you capped of the combi valves with the plates, did you use gaskets or any sealant on the plates?
Good point…they do have OE gaskets. OP, did you re-use yours or buy new ones? IIRC, 65vetteC6 was having issues with his block-off plates, but that may have been an issue with the plates themselves. Are you running the 034 plates, or did you find some of the old ebwerks plates floating around?
That’s my next step, should be able to get the logs done late one night this weekend. Do you know how I can log both banks at the same time for all the parameters? VCDS says I need a label file for controller 31 which reads from both ECUs simultaneously.
I capped with a set of ebwerks block plates and the OEM gasket.