Hi guys. I'm a long time lurker but first time poster. In the past, I've been able to find great answers to my questions just by searching here but this time around I'm not having as good of luck.

I have a 1998 LS 2wd "w" VIN with 134k miles.
It's had a little bit of a miss when cold and wet for some time now.
Last week the intake manifold gasket went and it started leaking antifreeze so I promptly replaced the gasket.
Now it idles and revs smoothly in park or neutral but stumbles really badly under moderate acceleration. The problem is somewhat worse when it has been wet outside but gets a lot better after about 7mi on the road. It never goes away completely though. If I get my foot into it a little bit it seems to stop missing and comes to life.
It's not putting out any error codes whatsoever.
Trying to fix this, I've replaced the cap and rotor, plug wires and PCV. I tested and cleaned the EGR valve as well as the MAP sensor and the MAF sensor.
The only thing that I know to be wrong that I haven't fixed is when reassembling the manifold, I broke a vacuum barb off of the "vacuum manifold" (no one that I've talked to knows what it's called. It simply plugs into the manifold and locks by turning about 45deg and has two outlets, one for the PCV valve and another that goes to a vacuum hose.) I don't know what all the hose coming off of it does other than assist the heat/AC mixing gate but it's been collapsed since this spring without any adverse affects other than an inoperable mixing gate. I tried doing a quick fix with some epoxy after not receiving any other ideas at the auto parts stores in town. That didn't work well and I just ran a screw into what is left of the barb to stop the vacuum leak. I really don't think that this is my problem and would feel stupid if it is but think that I should include it in the interest of full disclosure.
This morning, I took it for a spin around the block and discovered that it seems to run smoothly while in gear if I stay on the brake and rev it up but starts stumbling as soon as I let off of the brake.
Any advice or suggestions would be greatly appreciated!

 

Sounds like the distributor might be off a tooth or the timing is off.

 

Mr. Cat, you sir are a gentleman and a scholar.

It turned out that I needed to rotate the distributor one tooth clockwise. Since it idled well and my marks were lined up when I initially put it back together I never imagined that that's where I goofed.

Thank you thank you!

 

No problem, glad I could help!