An intake adaption system for internal combustion engines of vehicles employing an aftermarket intake air assembly including high capacity intake ducting and a low resistance air filter. Intake air sensors provide intake air condition signals of filtered intake air to the engine. A CPU includes a routine for modifying the intake air condition signals of the filtered intake air to the ECM. Tables alter the appropriate sensor signal or signals to correct for the calibration and predictions made by the ECM based on the original equipment. A first table translates the intake air condition signals from the intake air sensors indicative of MAF into the engine to provide actual MAF into the engine. A second table generates a pressure offset responsive to MAF into the engine to provide the ECM with a lower pressure value than actual, avoiding a diagnostic trouble code.