[SSGT Mustang]

One more thing.

Here's a tip when using the stock computer. Disconnect the wire to your O2 sensors, clean them very well, apply dielectric grease and reconnect them.

There are two connections from the harness. One on the front passenger side of the engine compartment, and one underneath the car, where the O2 sensors connect.

Condensation tends to accumulate in the connectors (particularly the one in the engine compartment), causing a lot of oxidation on the pins, which sends false readings to the computer. The computer uses those readings to measure against the value entered for air/fuel ratio, and will adjust to compensate for the difference.