I have a 91 Z28 TPI 305 with manual transmission. The vehicle is pretty much stock besides KandN air filter, Flowmaster exhaust, MSD wires, coil, cap and rotor, and a 52mm throttle body. I have replaced TPS, IAC, throttle body gasket, plenum gaskets, plugs, wires, coil, cap, rotor, ICM, ECM, O2 sensor, knock sensor, and EGR valve. I have since been messing with the car's timing. I had never timed a car before so I looked in the technical section of this site and found a great post. So I set my timing to what I thought was 10 BTDC instead of stock 6 BTDC but I read the marks wrong (can't see my marks and went by what I wrongly understood by post). I had actually set the timing to 16 BTDC as I thought each peak pointing towards front of car was 2 degrees instead of 4 degrees. Well, the car ran great at that timing - 16 BTDC. I since learned how to read the timing peaks and valleys and thought I better retime the car and set it to actuall 10 BTDC. Well she runs worse than she did when she was set at 16 BTDC. And actually, the further I retard her, 8 BTDC, and 6 BTDC she has worse acceleration and throttle response. I decided to look at the timing with the EST still plugged in and the car in open loop, as open loop is when she runs best. I was amazed that the timing mark was somewhere in the ballpark of the mid to high twenties BTDC. Of course this is an estimate as the timing gauge stops at approximately 16 BTDC. So does my car just like a huge advance setting like that or is there another issue I am not aware of?