electronic problem

i,ve got a 98 grand prix gt 3800 with about 147,000 miles on it. its been idling rough. I've changed the plugs and wires, coil modulator, and the main computer in the air box. i've also checked the coils, compression, injectors, and spark. they all checked out. with the old computer, the car almost had a mind of its own. all the electronics on the dash would do random crazy things without being touched. it also came up for codes for high RPM when idling and random/multiple misfire. With the new computer in, it still idles rough, but now it shifts violently between 1st and 2nd gears. the computer comes up with random messages and they keep changing. if anyone could help i would appreciate it

you need an ignition switch/harness assembly. AC-Delco part #D1491D. At the top of the Grand Prix forums is a tech section that shows the replacement proceedure.

Here's the link
http://www.automotiveforums.com/vbulletin/showthread.php?t=653340