Yes, remove the intake manifold. If you haven't done this, have NEW gaskets ready, along with new vacuum hose and some new fuel line. The old rubber lines get brittle and break.
This is a good time for "while I'm here, I might as well..." (none of this is very costly):
- replace injector grommets and o-rings
- clean the contact area on the engine wiring harness ground (bad contact here can lead to the 3,800 rpm stumble)
- clean out your EGR valve
- clean your aux port system, if this gets stuck open or closed from carbon/gunk buildup, you'll have power issues
- if you can afford to have your car down for a couple days, get injectors cleaned