Idle problem after double IC install

[johnny o]

I took 2 IC cores and welded em together. After install the car seemed to idle fine. The VAC used to be 18 at idle and now is about 15 and after leaving the car sit for ~3 min at idle it'll start to idle REAL rough and show VAC of 10 and idle 500-600ish. Car seems to build boost fine, about 10-11 psi and it used to get 11-12 but I expected a slight drop. Sometimes the car now also idles at 1500 and slowly works its way down to 1100 and just stays there and other times is slow surges between 1200-1400rpm. It used to idle fine at ~750rpm. I'm thinking it has to be 1 of 2 things: 1) there is a leak in the IC or the flanges but I used propane around the whole thing and the idle never went up. I didn't use any sealant on the flanges, should I use something? Again tho I used propane around them and nothing... OR 2) I didn't get all the metal **** out of the IC and **** got in my engine but I cleaned it out real good multiple times with gas, compressed air and a power washer and it looked real clean. I really doubt this tho cuz the engine runs real strong and I get 10+ psi when I get on it. Any ideas would be good.

[SeanMatteson]

Johnny,

It sounds to me like you've got a vacuum leak. Perhaps it's at some other joint. What else might have been disturbed when you swapped in the IC? You can use RTV Copper on those IC joints. You only need a thin layer.

I'd keep searching for a leak somewhere.

Best regards,

Sean

[92strokedbird]

You said that you checked for leaks using propane,maybe try brake clean instead with the tube in the spray nozzle.It will help to get the aerosol right where you aim versus propane which is harder to direct.Just a thought,did you check the seal between the intercoolers at the top and bottom.

[T1Bird]

Did you have the IC's pressure tested before hand?. Out of 3 IC's i took to get tested, all 3 leaked, and the 2 Ryan and I used for a double IC leaked big time, these IC's are the worst IC's out there according to most rad shops, very poor quality, leave it up to ford going the easy route!

[johnny o]

I never tested the other core that I got. Where are some places that could pressure test my double ic? The other core looked good and came out of a supposed running car. I will reinstall it with gasket sealant on the flanges and see if that helps and try brake cleaner.

[Ryan A Harris]

Any local RAD shop can do the leak test for you, should cost that much, maybe 10-15 bucks. But it sound like a VAC leak to me. If the cores leaked, you would have NO BOOST at all, it ALL would leak out.