Not the usual stupid idle prob PLEASE LOOK!!!

[BOBS90TURBO]

Here is the problem, When at idle I have a rough,missing, pop sound you can hear in the air filter, and a thump sound you can hear in the back of the engine, all the symptoms happen about 5 secounds apart.
Here is the crazy part, the car runs,boosts perfect,smooth and powerful as long as it is past 1200 rpm, these probs only happen at idle.
Here is what I have found, I sprayed carb cleaner around the intake on the back side of the motor and it reved up like I have a leak so i moved the battery and I can see a row of 4 vacum nipples and the two on the far right are missing, I can not find what they go to, they row of the 4 are past all the normall vac lines, in fact the 4 are very hard to see, I never knew thay were there untill yesterday, It seems when I spray the cleaner around that area the motor revs up. If it not the 2 missing vac lines causing this than any ideas on what or where could be leaking back around in the area. PLEASE HELP, I AM GOING CRAZY!!!

 

[BOBS90TURBO]

Oh-yeah, I just installed new 8mm Taylor wires,NKG plugs(gapped correct) new coil pack, ISC motor, TPS and blocked off the EGR. Also throddle body is clean.

 

[NOSNUSE]

I would have to say that there is a vacuum somewhere around the manifold you are on the right track to finding it, try around your EGR block off plate. The vacuum nipples are okay to leave lines off, they have never effected my car before.

 

[BOBS90TURBO]

So you are saying its normal to be missing the two right vacume lines on the right side.
Also I forgot to add that I have also replaced my ecu w/ rebuilt one.
Why can

 

[leet]

I'd get another ECU to test it with.

 

[BOBS90TURBO]

I have tried 3 different working ecu's with no change and even swapped the entire throddle body ISC,TPS ect.. off my 90 gst that idled perfect and still had no change. PLEASE I am out of ideas, I think I have tried everything.. I need some advise BAD!!!!!!!!!!!

 

[racer]

I have someting like this too but im N/A.Expecialy when i havent driven the car for like 3-4 days.For example I drive on 2nd gear with like 2000 rpm and sudenly I hit the accselerator and the car will bog or miss 2-3 times.It feeels like it wont grap and the tires are spining like there was a little rock or someting under them.It feels like when new driver try to drive a stick shift and the the car shakes cuz of not properly reliesed clutch.I hope that explanation is enough.My idle too when first start the car if it goes normal all of a sudent it ll be like rrrrrrrbourrrrbou like missing or someting.Then when it worms up doesnt feel that much.The car is very powerfull.No problem with the performance.(mods at profile).
If someone can help plz.I also cheked the ECU and "Stepper Motor" all fine.ISC is new.Engine has 123 000 on it.

 

[NOSNUSE]

Do you have a boost gauge, if so how many inches of vacuum are you pulling, should be around 17 to 19. Did you try and spray carb cleaner around the EGR block off plate? I would have to say that it is a vacuum leak of some sort. Not trying to sound like an a$$ but do you have the plug wires on the right way?

 

[BOBS90TURBO]

I will check my boost gauge in the morn, and yes I have double checked the plug wire order(I know it happens)..
Ok here is what I found out today,for sure I have an intake manifold leak just under the far bolt on the drivers side. I took a vacum line and pluged it into my ear and with the end of the hose I traced all around untill I heard the sound of sucking air. Can anyone tell me how hard this gasket is going to be to change???I will keep you posted on if this is the fix and Thanks for the advise so far.

 

[leet]

Thats gonna be fun to fix, and that WILL cause idle problems.

It's easier to take off the Intake Manifold if you do not have an A/C.

 

[Staged]

1st things first... there are 4 metal acceptance tubes under the intake manifold. You should have only 2 vacuum lines to them, the far inside 2. On the other side, under your coil packs and manifold, you will find the other end of the 4 metal tubes. There should be only 2 vacuum lines coming off of them, and they should be the inside 2. A lot of people will re-install the vac lines on one side or the other but onto the wrong metal tubes. Run both on each side to the 2 metal tubes closest to the motor, and you can't miss then. Otherwise, that is your vac leak right there.
If not, the block off plate IS your next best bet, and then there is also a chance to look at the BISS if the cap is still on it. That is on your TB. Look in other threads here for instruction on how to adjust this screw. You can't just go turning it. And that WILL affect your low idle. If the screw has popped out, it will also cause a vac leak.
Just a couple of quick hits for you to eliminate.

 

[BOBS90TURBO]

Ok, here is what fixed my problem (I hate it when people don't give the end results), I replaced the intake manifold gasket, also ported & polished the manifold, anyway after I put it all back together it runs as smooth as the day it was made, no more running rich or missing at idle at all, Thanks for the advise......