if it says running is 11, then there is no standing condition in the motor, hence you should not be running rich at all. The code's 31 means that the sensor on the back of the EGR drum is bad. I would replace it since it's not that expensive. The code 67 is meaningless since you got the engine started then the neutral saftey circuit shouldnt bother you.
Technically, you should be running a bit leaner if anything from the extra airflow due to lower exhaust backpressure if the EEC could not compensate. I leaned out when I installed my x-pipe.
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91 GT Carb conversion, holley 600 double pumper, edelbrock performer intake, FMS "C" drop springs, march 1000 underdrive pullies, crane 1.7 roller rockers, GT-40P headers, bassani x pipe, american thunder catback, FMS 4.56's, msd aL6, trunkmount battery, A/C eliminator kit, 3000 stall tci streetfighter, AOD with transgo kit, A+ servo, 300M hardened lockup shaft, kevlar bands and 28,000 gvw trans cooler, 3 core radiator, 300 lbs stripped with a full interior
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