What causes a low idle in a 1992 Chevy C1500 5.7L TBI?

Answer 1

While there are several items that control the idle on a 1992 Chevrolet C1500 5.7L TBI, I would suggest the following before I started replacing parts that may not need replacing.

Find someone who has a scan tool that can read live data from an On Board Diagnostic system.

If they have this type of scan tool then they should also have information available that will provide the normal readings of the system and various control devices. If something is out of specification you will know what needs to be investigated further and repaired or replaced.

Next I suggest checking the integrity of the electrical grounding network in the engine compartment especially, if the problem is intermittent and or you have noticed irregular readings on the instrument cluster. I have read that about 90% of the problems with GM products using the Throttle Body Injector system have been attributed to defective or no electrical ground.

Unfortunately I didn't read about it until after I had already spent hundreds of dollars replacing perfectly good parts that could not be returned for a refund.

Starting with the battery, make sure the connection is tight at the battery and on the engine. It should be grounded on the intake. Where the wire connects at the battery, there should be a smaller wire that is connected to the body. Next there should be a ground from the intake/block to the frame and then from the frame to the body.

If the engine is grounded well, the next step is to check the connections at the thermostat housing and elsewhere near the thermostat housing on the intake. Although I have yet to confirm this, it is believed these wires are ground wires for the Electronic Control Module which communicates with the Idle Air Control, Throttle Position Sensor, Coolant Temperature Sensor and Fuel Injectors.

Good luck.