Action Taken

WARNING: This page is about a different car, the 1990 Cadillac Fleetwood and 1990 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.

ECM turns on SERVICE SOON light for entire key cycle.

The ECM controls engine idle by increasing or decreasing throttle opening using ISC. The ISC will be active in controlling idle speed anytime throttle switch is closed. At vehicle speeds less than 6 MPH, ECM controls idle based on engine RPM. When vehicle speed is greater than 6 MPH, ECM controls idle based primarily on throttle opening (TPS) with adjustments to maintain a minimum engine RPM. Code E30 is designed to detect engine RPM out of limits high or low.

NOTE: Test numbers refer to test numbers on diagnostic chart.

Test Number 1) Check for proper throttle switch, brake switch and Park/Neutral switch operation. The ECM must receive accurate switch status information in order to control idle.

Test Number 2) Check for proper ISC motor operation.

Test Number 3) Many engine fuel and emissions system faults may cause unstable idle. If base engine idle is not steady, ISC may not be able to control idle speed to within 152 RPM of commanded idle speed.