Exhaust is extremely hot and has miss when running- Late timing or more serious? on 1994 Oldsmobile 88

Replace intake and plinium gasket for friend. Has had issue with running rough.. replaced plugs and that helped but still slight miss like timing and exhaust is extremely hot. late ignition timing? or could it be more serious? timing by computer only? Have diagnostis ran first? probably all of the above?

Asked by for the 1994 Oldsmobile 88
start with ck'ing for codes
10-4... scheduled for tomorrow. thank you