87 supra computer chip

Need help, I've searched scores of google hits, tens of forums, on every combination and not finding - where is the flipping computer chip ?
My 87 had new head installed by qualified mechanic who went out of business - new highway, eminent domain. Car ran really rough. Took to another reputable shop, $3,000.00 later, lots of stuff fixed but still runs rough - they're mystified. Alarm went off every time I unlocked door - friend of a friend at Toyata dealer says chip fried. Source of running rough ?
I'll replace it myself if I can find it. He said under driver seat - I took seat out, found a floor, no chip. Chilton's doesn't tell, Toyota site won't tell. Feeling foolish and frustrated. Help me guys?

Ehh, what forums did you search that had no information about this, I-supra? I really don't think your friends friend works at a Toyota dealership if he doesn't even know where the ECU is located. It's behind the glove box, remove it and you can swap it out. You must use the same year group and version (turbo, n/a) when you do swap the ECU out though. If you have a turbo you can only use a 87-88 turbo and likewise if it's n/a you must use 86.5-88 n/a. Before you go crazy with swapping out parts and spending more money I would suggest to pull the codes and see if the problem lies eslewhere.
http://www.cygnusx1.net/supra/techtip/engineerrorcodes.html
Also in the MKIII you aren't going to swap out or reprogram the chip inside the ECU, if you want to modify the ECU's signals you will have to use a piggy back system or go full standalone.

Thanks Dude.
I hear what you're saying about check error codes, but last place did that and came up nada. They have a good rep for competence. My big issue is run rough - I mean really rough. I was really hoping fried computer was simple solution and maybe they didn't diagnose chip itself ? Thanks for good suggestion and location.