Possible to have vacuum leak from lower intake gasket/lifter valley area?

[Ishman 306]

Recently My car has been acting like it has a vacuum leak:
1. choppy idle, would die--had to reset idle to what would be about 1200rpm if it were actually running right, but it still idles and sounds like its on 7 cylinders at like 600rpm.
2. bad gas millage
3. popping in exhaust every now and then
4. code 41,91 always lean condition.
I checked everything and changed about every sensor, and nothing helped, the problem got worse the longer of a trip the car went on. I sprayed carb cleaner around intake and it never raised rpm to show a vacuum leak, but i took the oil fill cap off, and disconnected the tube that goes from it to the TB, and there was a slight vacuum from inside the oil fill tube when i placed my hand over the opening. Could there be a vacuum leak on the bottom of the intake gasket in the lifter galley?

 

[Mustang5L5]

Yes.

My very first intake install turned out like this. Drove the car for a couple weeks in a poor state before tearing it off to see what a crappy job i did.

Thankfully i have gotten quite good at it now. One trick i learned to seating the lower intake vacuum-tight is to buy 2 bolts about 6" long that are the same size as the lower intake bolts. I cut the heads off and loosely threaded them into the block across from each other at the corners. I laid down the gaskets, RTV's up the front and rear and around the water jackets and lowered the intake down on the studs and then inserted the other intake bolts.

 

[Aryan15]

Were the heads resurfaced? Heard a story about an uneven head which wouldn't seal to the intake properly causing a leak.

 

[jrichker]

My favorite trick that saves time and effort is the stay in place gasket. Be sure that you scrape (don't use a wire brush) all the old gasket material off, then clean all the surfaces with acetone or MEK.

When the surfaces are clean, use weather strip adhesive on the head to manifold surface, and on the side of the gasket that mates to the head. Follow the instructions on the tube or can and when it gets tacky, press the gasket down on the head.

Clean the area where the rubber rails mount to the block in front and in the rear with more acetone or MEK and do the same trick with the weather strip adhesive that you did to the heads.

Coat the rubber seals and the gasket area around the water passages with lots of Blue Silicone gasket sealer and put it together. Wala! no leaks, and no gaskets that shifted out of place.

If you reuse the injectors from your old setup, a repair kit is available from most auto parts stores if needed. Coat the injector body "O" rings with oil before you use them and everything will slide back together. Take the other advice you got here and run with it.

Fuel injector seal kits with 2 O rings and a pintle cap (Borg-Warner P/N 274081) are available at Pep Boys auto parts. Cost is about $2.74 per kit. The following are listed at the Borg-Warner site ( http://www.borg-warner.com ) as being resellers of Borg-Warner parts:

http://www.partsplus.com/ or http://www.autovalue.com/ or http://www.pepboys.com/ or http://www.federatedautoparts.com/

Most of the links above have store locators for find a store in your area.

Use motor oil on the O rings when you re-assemble them & everything will slide into place. The gasoline will wash away any excess oil that gets in the wrong places and it will burn up in the combustion chamber.