I have a 1994 Ford 7.5 liter Gas engine, and I have OBD I code 538. "Insufficient RPM change during KOER Dynamic Response Test". What does this actually mean? Do I need to fix it? If so, how? The engine runs well unless it is over like 95 degrees and it is run hard, then when I slow down, it sputters and backfires until I either let it cool, or get it back to highway speed.

Any help would be appreciated, thanks.

 

During the KOER self test, the PCM commands the IAC (idle air control motor) to raise the engine RPM to the desired/calibrated speed.. If the engine speed isn't met you'll get a insufficient speed code.. Most times it's an issue with the IAC being restricted/clogged, sticking, or failing.. Without the IAC working in conjunction with the PCM commands, idle stability as well driveability to a degree can be a problem..

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