1989 C4 L98 rough idle, ECT display?
Thread Starter
Instructor
Joined: Oct 2016
Posts: 234
Likes: 10
From: Stockholm, Sweden
1989 C4 L98 rough idle, ECT display?
Hi,
Im diagnosing a 1989 C4 coupe with L98 engine. Engine was running rough at idle at all temps, with low RPMS, then all of a sudden high RPMS (12-1400rpm), then stabilize, or die. Sometimes you would hear a loud whooshing intake noise coming from the intake of the car.
Removed the IAC valve and found that dirty and with an uneven wear. Replaced it with a new one, and after a drive idle was good at normal engine temp. Still has issue when cold though.
I noticed the engine coolant display showed 18.2 Fahrenheit, or 8.3 degrees celsius when hot. Not 182 / 83 degrees, but with a decimal in place. Could it be the incorrect Engine coolant temperature sensor that's causing some issue, or is the sensor that supplies the cluster different to that connected to the ECM?
Thanks!
Im diagnosing a 1989 C4 coupe with L98 engine. Engine was running rough at idle at all temps, with low RPMS, then all of a sudden high RPMS (12-1400rpm), then stabilize, or die. Sometimes you would hear a loud whooshing intake noise coming from the intake of the car.
Removed the IAC valve and found that dirty and with an uneven wear. Replaced it with a new one, and after a drive idle was good at normal engine temp. Still has issue when cold though.
I noticed the engine coolant display showed 18.2 Fahrenheit, or 8.3 degrees celsius when hot. Not 182 / 83 degrees, but with a decimal in place. Could it be the incorrect Engine coolant temperature sensor that's causing some issue, or is the sensor that supplies the cluster different to that connected to the ECM?
Thanks!
Drifting
Joined: Jan 2021
Posts: 1,314
Likes: 384
From: Northern California
The sensor that supplies the temperature signal to the cluster is different than the one that supplies the ECM.
The sensor that supplies temp reading to the gauge cluster is in the right head, between the spark plugs #6 and #8 near the back of the engine. It has a single wire connecting to the harness.
However, that being said, your gauge should not be showing decimal points at all for the coolant temperature. It's more likely that the display just has the decimal point LCD stuck electrically (from the Volts reading when switched to that setting), and the real reading is 182F / 83C.
If you are chasing an issue you think is related to a faulty temperature sensor feeding the ECM (definitely possible), that sensor is in the front of the intake manifold underneath the throttle body housing.
The sensor that supplies temp reading to the gauge cluster is in the right head, between the spark plugs #6 and #8 near the back of the engine. It has a single wire connecting to the harness.
However, that being said, your gauge should not be showing decimal points at all for the coolant temperature. It's more likely that the display just has the decimal point LCD stuck electrically (from the Volts reading when switched to that setting), and the real reading is 182F / 83C.
If you are chasing an issue you think is related to a faulty temperature sensor feeding the ECM (definitely possible), that sensor is in the front of the intake manifold underneath the throttle body housing.
