It's normal. I don't remember the exact reason why, but the engine does it when it's cold. Don''t be worried! Mine does it almost every morning

 

same here, once i got to N or D it goes to normal idle RPM's

 

It is your jeep yelling at you for not having a heated garage. Mine does the same thing. Don't think it's anything to worry about.

 

If its cold outside it will hold a higher rpm to warm the Jeep up quicker until it reaches optimal temp and will slowly climb down.

 

If its cold outside it will hold a higher rpm to warm the Jeep up quicker until it reaches optimal temp and will slowly climb down.

The main purpose isn't to warm the car up quicker, in fact the additional 1,000rpm doesn't do much at all for temperatures without a load. And the temperature it does gain is merely a side affect from the real purpose:

as stated above... nothin to worry about... it's not just your jeep, its most big engines. Theres a reason they say to "warm up" your car before driving it. with the big 6.1, all the oil, coolant etc needs to warm up to a good fluid temperature. as its cycling thru the engine it's getting hot, then dumping back in the pan with the colder oil. but once it's all cycled thru and warm, you'll get that nice smooth idle. gotta remember. after sitting for a while, the engine oil as all dripped off the rods, cam, crank, pistons, etc back into the pan. all that stuff has to get lubed up again on start

It's not "most big engines," it's actually all modern fuel injected engines (Modern being post 1990ish). The high idle's purpose is not to warm up components at all, in fact it drops down to normal before oil temperature gets anywhere near operating temperature. The purpose is, as you eluded to, cycling the oil, but not warming it up. Also, stop listening to whoever has been telling you to "warm up" your car before driving it, probably the dealership so you have to buy a new motor faster. Warming up a car in the traditional sense, letting it sit at idle for 20 minutes, is godawful for engines. You should drive it as soon as you start it. Start it, put it in gear, and go. Do everything possible to keep RPMs low while driving, under 2-3,000 for sure, but get some load on the engine. Also, try to minimize cold shifting as well. You shouldn't redline it, or go anywhere close, until oil temps are north of 150.

Yes, exactly what you said. It's almost as I'm tapping on the gas pedal but I'm not. In the BMW 335i world this usually meant faulty injections. I'm just wondering if this is normal or should I be concerned at all. Thanks.

I doubt it's the same, the injection problems in the 35 series are stemming from the high pressure pump used for the direct injection setups, which have been problematic for the turbo 6s since they came out. As for it being normal, I can't honestly say I've ever observed my Jeep do it, but I put mine in gear as soon as I start it, so I wouldn't really know.

 

as stated above... nothin to worry about... it's not just your jeep, its most big engines. Theres a reason they say to "warm up" your car before driving it. with the big 6.1, all the oil, coolant etc needs to warm up to a good fluid temperature. as its cycling thru the engine it's getting hot, then dumping back in the pan with the colder oil. but once it's all cycled thru and warm, you'll get that nice smooth idle. gotta remember. after sitting for a while, the engine oil as all dripped off the rods, cam, crank, pistons, etc back into the pan. all that stuff has to get lubed up again on start

 

Programmed in: High idle / low idle....

Vehicles have been designed with high/low idle starts since the manual choke was removed in the 40s, 50s ... 60s? Not sure what year automatic chokes were installed on carbs or who designed it ...

They also used to have heat risers in the exhaust manifolds to assist with quicker warm ups...

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the ol '61 dart's got an automatic choke on her. Carter BBS 1-bbl. Auto-choke is run off of the exhaust manifold(#4 exhaust manifold runner), works sort-of like a thermostat. So I think they started the auto-choke around that time. And boy does it work like a charm. "runs like a good ol' slant" as the wayyyy old timers would say

OT: I think part of the reason the RPMs fluctuate has something to do with getting the oil pressure up a bit to get that cold, thicker oil flowing quicker. Cold, dry starts are hard on a motor, so the quicker to get it flowing the better. NOT sure if that's the reason behind it or not, but it would definately help longevity...So I'm sure the engineers may have that as PART of the reason for the fluctuation. I don't think the sole reason is to warm it up quicker, because it doesn't do it long enough in the cold to warm it up much faster than simply idling, since the motor is under zero load aside from it's own rotational forces.
My diesel does the same thing in the morning, but it will hold the RPMs up instead of bouncing up and down. But diesels rely on internal cylinder pressure and residual heat to get up to peak efficiency more quickly, as this is the nature of a diesel; sparkless combustion.. A cold diesel is a SLUGGISH, WEAK creature. Trust me. And seeing as how diesels have 2-3x the coolant that our rigs do, they can take a while to warm up completely, so you can't just jump in it and burn off.

 

Yeah I understand what you guys are saying. My concern is my rpms dipped down to 1k then went up to 1.5k then dipped down again to 1k went up 1.5k. Almost as if it was revving, I thought it could be a misfire bc the cold mornings. I don't think this is normal engine behavior.

 

He is having his idle fluctuate on cold starts.Like you are tapping the gas pedal off and on right?Mine does it every so often and I had no idea why,just kinda got used to it.
Usually about 45 seconds from start it will last.

 

Yes, exactly what you said. It's almost as I'm tapping on the gas pedal but I'm not. In the BMW 335i world this usually meant faulty injections. I'm just wondering if this is normal or should I be concerned at all. Thanks.

 

Thanks Aaron, yeah I am very familiar with the issues that are associated with the n54. Faulty injections, bad plugs, and a ****ty hpfp are the reasons I dumped the car. It was a blast to drive though. Anyways my jeep doesnt do this all the time, but it's done it 3-4 times. I'll just keep an eye on it. I thought maybe it was a known issues on these vehicles.

 

I think all internal combustion engines, when cold, need to be tickled...

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TPS or vacuum leak could cause jumpy rpms like that.

 

We don't have a TPS sensor, so I'm guessing that's not his problem.

The vacuum leak could do it, but with his symptoms, it doesn't sound like it, as a vacuum leak generally does not fluctuate the PM of the engine. Now if it's a vacuum leak that isn't static, like the size of the hole is changing all the time, that could do it. But it would still do it when his car is warm.

 

Really? If there is no TPS sensor, how does the ECM know what the throttle blade position is? EVERY EFI engine has a TPS sensor. Infact, Electronic throttle systems usually have 2, one reads 0-5 volts and the other reads 5-0 volts. It's part of the ETC safety system.

If the truck in questions is stock (and it appears to be if the mods in the signature are up to date), there is an issue and you should get it into the dealer. That is definetly not normal behavior. It may be a hardware issue (like a vacuum leak) or there may be an updated engine cal to address this. If the vehicle is modified (Cam, Heads, Supercharger, etc), it could be cal related.

J

 

I thought the purpose was to enrichen the mixture to get the motor to run at idle when cold.

My Race Hemi didn't have chokes (2x4s).. I had to start it and keep it running by feathering the throttle for a least 1-2 minutes, otherwise the idle would fall off and the motor would die.

These new fandangle Hemi's with EFI and throttle body, I'm wondering if the 6.1 has an Automatic Idle Speed (AIS) motor... if so, it could be the OPs problem.

.

 

Mine has been doing a the similar RPM surge and drop since the weather go really cold. Usually happens within a few seconds of a cold start up and lasts maybe 5 to 10 seconds. It sounds like the engine is surging but the RPMs are bouncing around 1200 to 1500 and then hold steady at around 1500 until the idle settles in around 800 after about 45 seconds. It doesn't happen when the engine or external temps are warm.

 

Ok I have been reading this and doing a search...EVERY time I start my car Hot / Cold my Idle goes to 1300 and slowly comes down,every start no matter the temp outside or if I just drove the heck out of it....answers..

 

Our cold start programs don't end until the ECT's hit 150* usually. Mine is 125* now on my Jeep. If you have a Trinity, watching your actual timing of Cyc. 1. You'll see you only run 4-7* of timing until your ECT hits 150* or whatever it's set at. Once you hit 150* ECT, you'll go up to the normal 20*-XX* that your tune is set at.

 

It's not only jeep,

I had MB ,Range Rover and Audi before and they all do same thing..

I usually don't drive until RPM drops.

It should drop after 1 or 2 min

 

The 'real' reason the engine idles up and down is because the Jeep SRT8 is a REAL MAN's car and like a real man, it teases and arouses the women by going up and down

 

This is probably the 3rd time it has happen to me. within the first 30 seconds of switching on the car, the rpms rise/drop until the car idles. What may cause this and should I be concerned? Thanks in advance!

Yeah I understand what you guys are saying. My concern is my rpms dipped down to 1k then went up to 1.5k then dipped down again to 1k went up 1.5k. Almost as if it was revving, I thought it could be a misfire bc the cold mornings. I don't think this is normal engine behavior.

Here you go print this out & take it to the dealer, should fix your problem. Had Dawn's done, doesn't do it anymore. Mine does it sometimes but haven't taken it in yet. Will wait till next time it HAS to go in. Don't like uninstalling then reinstalling the tune, lazy.

http://wkjeeps.com/tsb/tsb_wk_1802709.pdf

 

This flash fixed mine in January!

 

I had the same thing and the CHRYSLER tecks called it (searching for an idel speed). My fix was to get the predator updated from 8r20 to 9r12 and then redynoed and after that it has never done it again and that also got rid of the limp mode troubles i had now n then.