6.5 Idle

[DaveMcClain]

Is there any way to adjust the idle rpm of my 97 6.5?? 800 RPM's are too much. Would like to lower it to around 600. My Duramax Kodiak is at 600. Thanks. Terex

[JohnC]

Originally posted by Dave McClain:
Is there any way to adjust the idle rpm of my 97 6.5?? Short answer, no.

Longer answer: the PCM controls idle. I expect it's really not 800, but closer to 600. Usually this is becaue the alternator has been changed and has the wrong pulley. Easiest test is to find a scanner and read the RPM from the PCM.

[DaveMcClain]

The tach has always indicated 800 RPM. The PCM is the box on the truck, right?? And it is not adjustable?? Thx

[john8662]

PCM = Powertrain Control Module "the computer"

I'll agree that the tach could be off because of a swapped alternator pulley. The alternator is what operates the tachometer on a 6.5, so if a different drive pulley is installed on the alternator (reman) than it will affect the calibration between the alternator and the instrument because the drive ratio is off.

[JohnC]

Originally posted by Dave McClain:
The PCM is the box on the truck, right?? And it is not adjustable?? Thx Nope. Only external influence I can think of is the coolant temperature sensor. Still, compare the tach reading to the scanner reading.

[arveetek]

Originally posted by JohnC:
] Only external influence I can think of is the coolant temperature sensor.I was just getting ready to post that a fualty engine coolant sensor could cause the engine to idle too high. The computer monitors engine temperature and adjusts idle accordingly. There is a separate sensor for the guage on the dash.

Casey