Intermittents

Problem may or may not turn "on" the "SERVICE ENGINE SOON" light, or store a code.
DO NOT use the Trouble Code Charts in Section A for intermittent problems. The fault must be present to locate the problem. If a fault is intermittent, use of Trouble Code Charts may result in replacement of good parts.
^ Most intermittent problems are caused by faulty electrical connections or wiring. Perform careful check as described at start of Section B. Check for:
^ Poor mating of the connector halves, or terminals not fully seated in the connector body (backed out).
^ Improperly formed or damaged terminals. All connector terminals in problem circuit should be carefully reformed to increase contact tension.
^ Poor terminal to wire connection. This requires removing the terminal from the connector body to check. See Introduction to Section 6E.
^ If a visual check does not find the cause of the problem, the car can be driven with a voltmeter connected to a suspected circuit. An abnormal voltage reading when the problem occurs indicates the problem may be in that circuit. If the wiring and connectors check OK and a Trouble Code was stored for a circuit having a sensor, except for codes 44 and 45, substitute a known good sensor and recheck.
An intermittent "SERVICE ENGINE SOON" light with no stored code may be caused by;
^ Ignition coil shorted to ground and arcing at spark plug wires or plugs.
^ "SERVICE ENGINE SOON " light wire to ECM shorted to ground. (CKT 419).
^ Diagnostic "Test" Terminal wire to ECM, shorted to ground.(CKT 451)
^ ECM power grounds. See ECM wiring diagrams.
^ Loss of trouble code memory. To check, disconnect TPS and idle engine until "SERVICE ENGINE SOON" light comes on. Code 22 should be stored, and kept in memory when ignition is turned off. If not, the ECM is faulty.
^ Check for an electrical system interference caused by a defective relay, ECM driven solenoid, or switch. They can cause a sharp electrical surge. Normally, the problem will occur when the faulty component is operated.
^ Check for improper installation of electrical options, such as lights, 2-way radios, etc.
^ EST wires should be kept away from spark plug wires, distributor wires, distributor housing, coil, and generator. Wire from circuit 453 to distributor should be a good ground.
^ Check for open diode across A/C compressor clutch, and for other open diodes (see wiring diagrams).