High Idle on start up - Dodge Challenger Forum: Challenger & SRT8 Forums
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post #1 of 9 (permalink) Old 06-04-2019, 08:32 AM Thread Starter
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High Idle on start up

New Hellcat owner, on cold start up my idle goes up to 1750 rpm and then slowly drops back to approx. 750 rpm. Is this high rpm normal for the hellcats? My scatpack didn't rev this high on initial startups.
I couldn't find any information about this in my searches on this site.

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post #2 of 9 (permalink) Old 06-04-2019, 08:48 AM
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Appears to be normal. According to this 2016 stock HC tune startup idle should be around 1700rpm for coolant temps below 104F. See attached image of elevated idle table.
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2015 Challenger RT+ (non-STP)
8lb Magnuson w/ Innovate PSB-1 wideband/boost/shift light gauge
Corsa extreme (2.5")
4" Aluminum one-piece driveshaft
Hellcat bottom airbox
Stainless Works LT headers (2" primaries)
Barton shifter assembly w/ Lou's short shaft and Speed Dawg knob
Comp Cam 7929 & 7748 push rods (gives slightly more lifter preload)
A2speed aluminum coil and valve covers (built in catchcan)
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post #3 of 9 (permalink) Old 06-04-2019, 08:59 AM
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Different engine but my scat revs high on cold start also.

2019 wide body Scat
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post #4 of 9 (permalink) Old 06-04-2019, 10:59 AM
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Scats don't rev as high on start up as the HCs do.
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post #5 of 9 (permalink) Old 06-04-2019, 08:14 PM
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Is that top number seconds?
I will look at it closely tomorrow morning but that looks right.
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post #6 of 9 (permalink) Old 06-05-2019, 07:42 AM
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Quote:
Originally Posted by Decay View Post
Is that top number seconds?
I will look at it closely tomorrow morning but that looks right.
Basically idle is commanded from this table at first based on engine temp and how long the engine has been running. The PCM then refers to other tables to determine final idle once the car hits optimum temp. On my 2015 RT manual, the P/N or Manual w/AC (took a couple of tries to confirm this table controls the final idle).

BTW I bumped up my elevated idle in the 0 and 3.2 s engine run time columns to give the can a nice startup rumble which tapers down abruptly. It's like starting the car with a little bit of pedal that you release quickly.
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post #7 of 9 (permalink) Old 06-12-2019, 09:41 AM
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I have a ‘15 Hellcat...same startup rev sequence from day one...all is well.
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post #8 of 9 (permalink) Old 06-12-2019, 10:15 AM
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Quote:
Originally Posted by redcat15 View Post
I have a ‘15 Hellcat...same startup rev sequence from day one...all is well.
Yes, that has been established as the HC calibration is programmed for high idle at start-up:

Hell Cat elevated idle map


Scat Pack elevated idle map
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post #9 of 9 (permalink) Old 06-12-2019, 12:07 PM
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What ChallyTatum said. I had thought my Hellcat idle dropped rather quickly like my cars before it, but paying more/closer attention I find it does take longer to for the Hellcat engine RPMs to drop.

But the RPMs do drop. Might note where I live and drive ambient temperatures are mild (at least at night; last couple of days we've had triple digit heat but the Hellcat has remained parked under a carport and I have used my other car) so in the AM the car/engine is not that cold and coolant temperature starts out pretty "high" and comes up pretty quick. I have not experienced the Hellcat in real cold temperatures and I don't know what the idle speed would do in colder temperatures.
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  Dodge Challenger Forum: Challenger & SRT8 Forums > Model Specific Discussion > Dodge Challenger SRT8 Specific > SRT Hellcat 6.2L Supercharged (2015 - )

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