just changed intake manifold and a big problem appears....

What are the shape of the intake ports (teardrop or square)? The PI intake is square where as the Non-PI is a round tear drop shape.

What did you do about gaskets? Some of the Dorman units have built in gaskets. If you added gaskets, I could see that causing problems.

Is the coolant cross over installed in front?

Pictures of the old and new intake?

Why did you changed manifolds? And if it doesn't seem right, stop and ask questions then before proceeding and possibly doing more damage... (Sorry, don't really mean to pop you with those right off the bat, but it's those types of lessons that we've all learned at one time or another)

You say the intake tube is like it's getting sucked by a vacuum and is choked like it can't get any air? Is the tube collapsing? You'd need a restriction at the end of the tube (like putting your hand over the end of a vacuum cleaner hose) to cause that - did you perhaps suck a rag up into the air cleaner? I imagine that would make more noise too from the air filter area. There normally shouldn't be any significant vacuum in the intake tube, especially at idle - the only thing between it and open atmosphere is the air filter and the MAF - as RPMs and loads increase and air is moving faster through the tube, there'll be a bigger pressure drop inside of it but it shouldn't be so much that you'd see it if you're in the driveway revving it up by hand. Problems with gaskets or intake port mismatches downstream of the throttle body would cause less air to be moving in the intake tube - either through vacuum leaks or restrictions preventing the engine from drawing as much air - so there'd be even less negative pressure in the intake tube than normal. You may hear the sounds of those restrictions travel back up the tube though. More detail as to what you're seeing and hearing would help.

There are two replacement intakes for Mustangs from Dorman. One for 96-98 (NPI) and one for 99-04 (PI). It's possible, I suppose, that they gave you the wrong one, which would cause vacuum leaks at each intake port as the NPI ports are smaller and rounder and those gaskets would not completely cover the PI ports on the cylinder heads. You'd probably hear some air hissing from that and there'd definitely be all sorts of driveability issues.

Here's the intake port shapes that Wmburns is describing - the two intakes on top fit PI cars (like yours) and the bottom one is an earlier NPI intake.


The fuel injector and spark plug locations don't really change from the NPI heads and intake to the PI heads and intake so even if you did have the wrong intake, it shouldn't block those. There is some wiggle room between the bushings in the intake and the mounting bolts so make sure you line everything up before you start tightening the bolts down.

Can you describe this loud sound it's making?