I'm restoring a 1991 Buick Riviera the suspension work is done. I thought that I was through with the engine it has new sensors,the water system is all new. During this time I'd sent the insturment cluster out to be rebuilt. It was suppose to be back before the was done it never happened. When I got it back I put in the car and what do I get engine codes 3 of them. The computer had already been replaced , I'm pulling codes 21 26 41. the that worries me is code 26 that is a quad driver which a computer chip feeding information to 4 different locations. my question is what is location of this chip and could this chip be driving the throttle position sensor and thecam sensor which would mean I need a new computer I'm trying to get it smogged. Thanks much. P.S. When I cleared The codes the engine light came back on. Ichecked the codes again and got a 21 And 41. the car was running badly, a throttle position sensor adjustment took care of that. I pulled codes again and had all 3 of them back. I'm looking at that computer hard now and my diagnostic tool but when I hoop up my OBD1 it throws code 12 which indicates that it is running fine. Any help would be appreciated. Thanks much Rick in Sacramento.