Engine Performance Problem - Odor, Surge, Fuel Economy Or Emission Problem

If the "CHECK ENGINE" light is not on, normal checks that would be performed on cars without the system should be done first.
If the alternator or coolant light is on with the "CHECK ENGINE" light, they should be diagnosed first.
Inspect for poor connections at coolant sensor, mixture control solenoid, etc. Also check for poor or loose vacuum hoses and connections. Repair as necessary.
If there is an intermittent "CHECK ENGINE" light, but no trouble code is stored, check the following:
- Check ignition coil to ground and check for arcing at spark plug wires or spark plugs
- Check battery-to-ECM terminals"C" and "R".
- Check ECM Terminals "A" and "U" to ground.
- Check ECM Terminal No. 19 to distributor, including tach filter.
- Check for a loss of trouble code long-term memory memory. Grounding the dwell lead for 10 seconds with the "TEST" lead ungrounded should produce a Code 23. This Code 23 should remain after engine is turned off and ignition switch is turned to the "RUN" position. If not, ECM is defective and must be replaced.
- Check that the EST wires are kept away from spark plug wires, distributor housing, ignition coil and alternator. Wires from ECM Terminal No. 13 to distributor and the shield around the EST wires should have a good ground.
- Check for an open diode across the A/C compressor clutch.
If the customer complaint is detonation (spark knock), check the vacuum sensor output. See VACUUM SENSOR OUTPUT TEST. Also check TPS enrichment operation. See TPS ENRICHMENT CHECK flow chart.
If the complaint is poor performance and/or fuel economy, perform CODE 42 - EST CKT CHECK.
If the customer is experiencing poor full throttle performance, refer to CODE 21 - TPS CKT CHECK.
If the complaint is intermittent no-start, check for incorrect pick-up coil or ignition coil. See CRANKS, BUT WON'T RUN flow chart. Also check for intermittent ground connections on the ECM.