What's your idle RPM?

shovenose

Original poster
Member
Apr 24, 2016
318
SF Bay Area, CA
I'm curious what your idle is when your Vortec 4.2 is warmed up. Mine seems to run OK at idle of 500-600 but that seems lower than other GMs I've owned. Is this normal? If that idle is unusually low, perhaps it's causing an intermittent hesitation upon applying throttle off idle especially on a warm start. Thank you for any input.
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
Seems about right to me. i think mine is 600-650ish
 

DocBrown

Member
Dec 8, 2011
501
Yep, 600. My old TB 4.2 was 600, my Sierra 5.3 is 600, and my 2.4 HHR is 600. It should be a steady 600. If it's bouncing around a bit then you might have a worn O2 sensor or other faulty emissions component. You won't necessarily get a code for this.
 

Sparky

Member
Dec 4, 2011
12,927
~600 is normal.
 

dmanns67

Member
Apr 3, 2013
32,979
Ohio
My 4.2L at operating temp will idle anywhere from 600 rpm to 610 rpm. Usually jumps around in that range. I can see this using my TorquePro app.
 

Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
Here's the commanded idle speed table, based on engine coolant temp, from HP Tuners :twocents:

HP%20Tuners%20Idle.jpg
 

RTTBLT1

Member
Jan 25, 2016
512
Louisburg, KS
Using the Torque App here too and with the 4.2L Engine...and I get around 600-625 at Idle when Engine is at normal (210F) operating temperatures.
 

Sparky

Member
Dec 4, 2011
12,927
That's old school stuff though now. My Silverado with the 5.3 idles around 600-ish too I think.
 

shovenose

Original poster
Member
Apr 24, 2016
318
SF Bay Area, CA
All of the later 350 V8's (5.7 Vortec) that I've come into contact with seem to idle at around 900.
Yup! I've owned a couple Vortec 350s and a TBI 350 and all idled higher, which is why I was curious. Actually, now that I think of it, the Vortecs idled higher than the TBI.
 
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