Ok, high vacuum at idle, when you crack the throttle open, vacuum is less. (higher pressure in the manifold.) That's normal. Vacuum climbing shortly thereafter is probably from the engine wanting more air than the throttle body is willing to supply at that point. So, manifold pressure goes down.... (higher vacuum reading)

How's your air filter? PCV valve?

 

Again, you're looking at the gauge backwards, vacuum falls when he hits the gas then rises, normal.

 

here's a pic of the gauge in question:

http://www.harborfreight.com/fuel-pu...ter-93547.html


The top of the gauge is for the fuel pump, the bottom of the gauge does engine vac.

Zero is at the far left and the needle swings down and to the right to top out at 28"hg.

 

Filter due to be cleaned, but it's not like it's wrapped in leaves.

PCV is brand new, per page 2 or 3.

Here is what I've tried:

New coil, because I thought it was a misfire and coil read out of spec, no improvement.

Twisted distributor from +2 to -2 because I thought I heard a backfire through the TB and that fixed it before, no improvement.

New TPS, no improvement.

New MAP sensor, no improvement.

New IAC, no improvement.

Tightened all bolts on the intake manifold, tb riser, and tb, no improvement.

Every time it stutters, the vac drops and the injector pulse width goes up, dumping fuel.

 

Have you used carb or brake cleaner to check for vacuum leaks? (that's sure what it acts like....) if you don't find anything obvious, try capping off the lines that run to the reservoir under the cowl, and the heater controls.

 

I was thinking I'd pay a local shop to hook it up to the smoke machine and be done with it. If that doesn't find the leak, I'm in trouble.

 

Maybe unplug the IAC and try driving it?

 

Hey there, my 98 had a similar random stumbling/stutter problem after stops, and at slow speeds (pulling away from a light etc). You could never predict it, some days it wouldn't act up at all, and others it would happen frequently. I took my truck to my mechanic and it only frustrated him, he couldn't figure out what was causing it...so the problem remained (I spent about 8 months battling this). I had always run 87 Octane in my truck with no issues, so I did not figure it would consistently be bad gas. However, I decided to run a tank of 89 through it and had no stumbles...so I continued to run 89, and have not had a stumble since! Very interesting...not saying you have the same issue as you guys are talking vacuum....but a simple fuel change might be worth a shot if you are running low grade...worked for me!

 

Your right, now that I see the better pic of the gauge. I agree, it looks normal.

 

Hell at this point anything is worth a shot, I'm running 93, but I'll try different gas station.

I did switch stations recently, maybe they have a problem with water in the gas tanks. When the engine heats up, it's more likely to misfire.

I'm up for anything at this point.