Engine idle issues when warm or when I drive

Hello my name is Dave.

My first suspect is the coolant temperature sensor, it's located by the thermostat housing. It is inexpensive and a very common problem with the early GM systems, a lot of times without a check engine light. When they go bad it will usually run decent when started but as the engine warms up and the ECM doesn't know it it due to the sensor it runs too rich.

If it was my vehicle I would replace the sensor regardless. If you can replace the sensor and let us know the results we would appreciate it. We look forward to hearing back from you and thank you for using 2CarPros!

Hi,

The coolant temperature switch is located on the left side of the engine (driver's side) and between the first and second spark plug. See pics 1 and 2.

First, here is a link to help with the procedure:

https://www.2carpros.com/articles/coolant-temperature-sensor-cts-replacement

Here are the directions for replacement specific to your vehicle:

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1989 Chevy Truck K 2500 Truck 4WD V8-350 5.7L
Coolant Temperature Sensor (CTS)
Vehicle Powertrain Management Sensors and Switches - Powertrain Management Sensors and Switches - Computers and Control Systems Coolant Temperature Sensor/Switch (For Computer) Service and Repair Procedures Coolant Temperature Sensor (CTS)
COOLANT TEMPERATURE SENSOR (CTS)
The coolant sensor must be handled carefully. If sensor is damaged, fuel injection operation will be affected.

1. Disconnect battery ground cable.
2. Drain coolant from radiator so level is below sensor.
3. Disconnect coolant sensor electrical connector.
4. Carefully back out coolant sensor and remove.
5. Reverse procedure to install.

I hope this helps. Let me know if you have other questions.

Take care and God Bless,

Joe