Oscillating Idle

[Quattro8880 at aol.com]

I just rebuilt the head on my 88 80q with much success. I have a few questions though.

The car sat around for 3 or 4 months (over the winter) while this occurred. I did drain the block of both oil and coolant, but did not drain the gas tank.

I got the car started and it seemed OK. I took it to work yesterday, about a 12 mile trip. It totally died out about 8 miles down the road. I coated to the side, checked the oil and antifreeze - both normal.

I got back in and it started back up - fine. Drove another 1/4 mile died. Coasted to a stop - checked everything again, including loose plugs and hoses. Got in and it started back up. Ran the rest of the way to work and home fine. I chalked it up to bad gas.

Filled it up with premium this morning and no stalling to work. Seemed good UNTIL....

I warmed it up before I left today because it's a little chilly in NY today. Warmed up to normal temp and off I went. Got 10 miles into my 12 miles trip and it died again. Go through the routine - everything seems fine. It started up and I got home.

Now the idle is jumping between 600 rpms and 1200 rpms every second, if not less. Up and down, up and down.

Unplug the ISV and it makes no difference - so there is no signal getting to the ISV right? 

One last thing - I installed a new catalytic convertor as well, but I reused the old one with about 30,000 miles on it. A mistake in hindsight, but could this be the problem? In addition, does anyone have an old junker that they would give or sell me the old harness from - mine is really in bad shape.

TIA