Help Needed - Slight Vacuum Leak

Hello All:
Okay, over the weekend I replaced my intake manifold, and the job went very smoothly (and I hope to post photos soon).

I thoroughly cleaned the intake mounting surface. I mean THOROUGHLY cleaned it.

I torqued the manifold mounting bolts down to the correct setting, and I tightened the bolts in the proper sequence.

The car runs very well, but I am now trying to chase down what appears to be a slight vacuum leak.

If you accelerate gently, you would never know the car has a problem. Acceleration is smooth and consistent.

But if you give it gas even a little bit aggressively, she stutters and shakes and stumbles.

What is interesting is that even during aggressive acceleration, she will eventually start running smoothly....but she DOES NOT like it when you first starting putting the pedal to the metal. It's almost as if she is putting up a fight and then "gives up" and gets smooth again. The stumbling/stuttering never continues for long.

Any clues where I should look? What are the most common locations for vacuum leaks on this engine?

We have to assume that it's not the intake manifold (at least for the moment).....

THANKS EVERYONE!!

shaunspengler:

I checked all of the vacuum lines you mentioned. Everything is hooked up correctly, nice and tight.

I'm starting to suspect that I have a bad spark plug wire for the #4 cylinder (that's the one that's misfiring). I will also check my PCV valves.

trinity_gt:

I checked and double-checked the fuel rail vacuum line, so I know it's not that.

As for the fuel pressure sensor, I will check that next.

Someone has also suggested cleaning the MAF sensor, which I have never done, I'm ashamed to say.

TripleBlk:

I actually changed that hose a while ago. I replaced it with nice stout heater-grade hose. But thanks...that would definitely have caused a problem if it had come undone!