I need help with a stumbling/idle problem

[pantera1683]

Okay, for the past month or so I have been having an intermittent problem with the Z stumbling while cruising. I first noticed it while driving at constant highway speed on a trip from Dallas to Houston. It would stumble or "hiccup" for a few seconds at a time as if it wasn't getting enough fuel. It did this for about 1/2 an hour and went away. I pulled the plenum and changed the alternator, coils and wires. I checked all the vacuum hoses and added zip ties to the connections. The hiccups would pop up very rarely after that.

On Vets day I got caught in a downpour and the stumbling came back, but this time it had a hard time accelerating from a stop. It struggled to accelerate until I stabbed the gas pedal, then it would accelerate normally. I pulled over and it shut off. It did start back up immediately after and seemed to work fine after. Yesterday, it was driving fine until I got a block from home, the stumble came back coming trying to accelerate from a stop and the idle went to 1200 rpm and kept rising to 2000 rpm.

Here is some background on the car. It is a 94 with 36k miles on it. It sat for several years before I purchased it earlier this year. I bought it with 33,5k miles and the PO only put 2k miles on it in the preceding 2 years. The fuel filter and plugs were all changed earlier this year.

Any ideas?