LIMP HOME MODE

I have an 89 GTA Trans Am w5.7L TPI motor. I'm at a loss and am in need of some help and guidance. The car according to the snap-on scanner I used is running in "LIMP HOME MODE". The first problem is there are no codes in the computer. I've done the tap test on the ECM and MAF. There was no change in running. I've checked to make sure the SES light is functioning and it is. The car in the past 2 weeks has a new distibutor, cap, rotor, plugs, wires, coolant temp sensor, and Mass Air Flow sensor(MAF). The EGR vavle checks to be in good working order, the IAT sensor has the correct resistance. Any help in another direction would be greatly appreciated. Again the scanner says LIMP HOME MODE and lean O2 sensor. Thanks