Checking the Basics

WARNING: Be sure to apply parking brake and/or block wheels before performing any test with the engine running.

Check and Record Idle RPM
If vehicle is equipped with an automatic transaxle, test and record idle rpm when the vehicle is first brought into shop, to assist in diagnosing;

- Engine Stalling
- Creeping
- Hard Shifting

SEE COMPUTERS AND CONTROL SYSTEMS/ TESTING AND INSPECTION/ PROCEDURES/ COMPONENT TESTS/ THROTTLE BODY MINIMUM AIRFLOW TEST.

NOTE: Prior to any teardown, repair or component replacement, the following steps should always be considered.

Battery State of Charge
Batteries in a state of partial discharge can have a dramatic effect on control units and related components.

Positive Battery Cable Integrity
All B+ connections must be in perfect condition for trouble-free electronic system operation. Refer to WIRING DIAGRAMS for B+ connections and splices.

Fuse Integrity
Fuses are employed to prevent possible damage to electrical components and wiring harnesses. The fuses and their connections must be without dynamic resistance. Dynamic resistance can only be checked using the voltage drop method of testing.

Negative Ground Connections
As all electrical circuits are a circle, all B- connections must also be checked and verified to be in perfect condition.
- A poor "common" ground point will cause seemingly unrelated systems to influence one another.
- High current systems which encounter a poor "common" ground can back feed through other electrical systems causing unusual operation and perhaps inexplicable component failure.

As with the B+ side of the electrical system, the ground side should be checked dynamically using the voltage drop technique.

Throttle and Speed Control Cables
Metal cables attached to the engine or transmission which appear overheated and/or discolored indicate the need to thoroughly test all ground connections.

Power Supply Relays
The system relay as well as relay connector can be a source of intermittent operation which will not set a trouble code.

Crankshaft Position/Distributor Pick-up
Hall Effect switches should be checked statically and dynamically. Physical mounting and condition of the sensor must be assured.

Secondary Ignition Components/Wiring
The secondary ignition system should be checked visibly as well as with a suitable engine analyzer and scope. All components should be examined for tight connections and freedom from carbon tracking, moisture and corrosion.

Fuel Delivery
Fuel delivery must begin at once when cranking and fuel pressure at fuel injectors must be within specifications.

Fuel pressure must be maintained between the fuel pump outlet and the pressure regulator after engine shutdown.

Valve Clearance and Spark Plugs
These two service items, if out of specification, can significantly impair engine performance.
- Valve adjustment procedures should be strictly observed.
- Spark plug type, condition and gap must be as specified by manufacturer.

Air/Fuel Ratio
When troubleshooting idle quality or driveability complaints, it is necessary to consider the following:
- Injector spray pattern quality
- Presence of vacuum and/or air leaks
- Evaporative purge system
- Excessive engine oil dilution
- Contaminated fuel or unapproved additives
- Carbon build-up