I feel your pain! I just did my UIM on my '98 this week. My car "hydro-locked" and wouldn't restart at all. There are great procedures to do this online, I am sure Little Hoov hooked you up. Is the car already converted to the "green antifreeze"? I had switched mine 2 months back when I did the Water Pump. Make sure you replace the UIM with the Dorman kit # 615-180 ($150.00@Autozone). This is the better than original design. This is the kit that all the reputable shops go with. Be sure to change your plugs($7/ea) and oil, and let the car idle for 15 minutes so that residual coolant burns up(will blow white smoke a little bit). Good luck keep us posted.
P.S. the kit tells you to torque the UIM Plenum in a specific order, 3 times around, to increased "inch pounds". This tool has to be adjustable from like 24 to 90 "inch pounds". Azone didn't carry this tool so i had to improvise.