Abstract: An idle air control system diagnostic for an internal combustion engine which utilizes RPM, engine timing and intake airflow measurements to detect the presence of idle RPM faults and eliminate or verify the idle air control system as the fault source. Engine idle RPM is measured and compared with a commanded idle RPM, and if within a predetermined range, an idle RPM fault exists and one of two additional tests (non-intrusive and intrusive) is conducted to determine whether the idle air control system is the source of the fault. In the non-intrusive test, intake airflow is measured and compared to a predetermined intake airflow value, and if not within a predetermined range, the idle air control system is determined to be the fault source. In the intrusive test, variations in intake airflow (or intake manifold pressure) are measured in response to variations in the movement of the engine throttle-bypass airway pintle.

Abstract: A system and method determines the rotational speed of a rotating member by determining speed from signals having a frequency directly proportional to the rotational speed. The system provides for the estimation of rotational speed even if no speed signals are detected over a sampling interval.

Abstract: A system and method for determining the rotational speed of a rotating member is described that determines speed from signals having a frequency directly proportional to the rotational speed. The speed signals are counted during each of successive sampling intervals. At the end of each sampling interval, the rotational speed is determined based on a calculation interval that is the time interval from the next-to-last speed signal generated in the prior sampling interval to the last speed signal generated and the number of speed signals occurring in the calculation interval. The resulting overlapping calculation intervals minimize the influence of one speed signal on successive determinations of rotational speed.