Idle related

[dwhiskie]

Ok, my car idles pretty good at 1000rpms but when I turn on the headlights the idle goes up about 400rpms and stays there untill I shut the lights off then it goes back down to 1K. I cant figure out why anything electrical would influence the idle. Any ideas??-All my grounds are good.

 

[Black 93 Fox]

Cause the motor is put under more load. It has to spin the alt faster to make more power which raises the RPM's. I wouldnt expect it to raise 400 tho.

 

[jrichker]

Possible bad alternator power ground or low output from the alternator.

The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges. Any car that has a 3G alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects.