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Slightly Rough Idle

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Brie94

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Discussion starter · #1 ·
Hi Everyone!
I have a 2018 Jeep Grand Cherokee Limited. It's the 4WD 3.6L and there are NO CODES. I have a slightly rough idle when in park and while stopped with my foot on the break. One weird thing I noticed is the harder I press my foot on the break, the more I feel that vibration (RPM'S also slightly drop which I am unsure if this is normal). I replaced a vacuum hose that commonly breaks on these and also tried the trick to reset the throttle position sensor. Rough idle still remains....my next steps are to replace the air filter, fuel filter, clean the throttle body and try fuel injector cleaner. I'm really at a loss being there are no codes and the car runs and shifts as normal once I am driving. This has been going on for almost a month...I was hoping it would throw a code to help diagnose the issue but I guess it wants me to struggle...jeep life lol. Has anyone else experienced this issue? If so what was the problem? Any tips, advice and ideas are appreciated!
 
#2 ·
Before you try your next steps, check your motor mounts. They are fluid filled and fail. If you don't see any fluid leaking out of them, open the hood and have some one else put the Jeep in gear, put their foot on the break, and give it some gas. If the motor moves right or left more than an inch or so, you probably need new motor mounts. I started to go down the same steps as you, when I had similar symptoms, then checked the motor mounts and they were bad. Hopefully you have a Mopar "extended warranty" to cover the cost.
 
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Discussion starter · #4 ·
jgcrp1 said:
Before you try your next steps, check your motor mounts. They are fluid filled and fail. If you don't see any fluid leaking out of them, open the hood and have some one else put the Jeep in gear, put their foot on the break, and give it some gas. If the motor moves right or left more than an inch or so, you probably need new motor mounts. I started to go down the same steps as you, when I had similar symptoms, then checked the motor mounts and they were bad. Hopefully you have a Mopar "extended warranty" to cover the cost.
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I will give this a try! Thank you.
 
#6 ·
"I replaced a vacuum hose that commonly breaks on these". Which vacuum hose is this you're talking about? I'd like to check mine on my 2017. I am hearing, not really feeling yet, but hearing a vibration when in Drive at idle like at a stop light. RPMs are down around 6oo or so.
 
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#7 ·
I had the same/similar issue here, in my case was the driver side engine mount, there was no sign of oil leak, but when I put it on D and rev it with left foot on brake, the engine moved more than 3 inches.

I changed all the 3 mounts (2 engine 1 for trans) all SKP cheap from rockauto and solved the vibration.
 
#8 ·
jgcrp1 said:
Before you try your next steps, check your motor mounts. They are fluid filled and fail. If you don't see any fluid leaking out of them, open the hood and have some one else put the Jeep in gear, put their foot on the break, and give it some gas. If the motor moves right or left more than an inch or so, you probably need new motor mounts. I started to go down the same steps as you, when I had similar symptoms, then checked the motor mounts and they were bad. Hopefully you have a Mopar "extended warranty" to cover the cost.
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At about what mileage do mounts tend to start to go bad. I have this issue as well with about 63000. Just started about 2 was ago.
 
#9 ·
casiasalfred4 said:
At about what mileage do mounts tend to start to go bad. I have this issue as well with about 63000. Just started about 2 was ago.
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Not sure what mileage they went bad, but had them replaced at 99.5K just prior to my MaxCare expiring. Have seen others on this forum with much less mileage than mine when they had to replace them. Not sure if that's due to temps (hot or cold), driving style, etc.
 
#10 ·
Brie94 said:
Hi Everyone!
I have a 2018 Jeep Grand Cherokee Limited. It's the 4WD 3.6L and there are NO CODES. I have a slightly rough idle when in park and while stopped with my foot on the break. One weird thing I noticed is the harder I press my foot on the break, the more I feel that vibration (RPM'S also slightly drop which I am unsure if this is normal). I replaced a vacuum hose that commonly breaks on these and also tried the trick to reset the throttle position sensor. Rough idle still remains....my next steps are to replace the air filter, fuel filter, clean the throttle body and try fuel injector cleaner. I'm really at a loss being there are no codes and the car runs and shifts as normal once I am driving. This has been going on for almost a month...I was hoping it would throw a code to help diagnose the issue but I guess it wants me to struggle...jeep life lol. Has anyone else experienced this issue? If so what was the problem? Any tips, advice and ideas are appreciated!
Click to expand...
I have the exact same problem. I thought I was going nuts with the brake pedal thing. but it does the same thing. Did you ever figure out what it was
 
#12 ·
69000 miles, mounts are good. with vehicle in drive AC off, if you barley have enough pressure on the brake pedal to keep vehicle from rolling the rough idle is very slight. the harder you push on the brakes the stronger it becomes. If I put the E-brake on with vehicle in drive and let off the brake pedal it goes away. as soon as I start to push the brake pedal down the idle drops about 50-75 rpm and it idles rough. I did notice that the vacuum pump turns on when this happens too. other than that, the truck runs and drives great. it started about a week ago. I could most of the time hardly tell the engine was running at idle before.
 
#14 ·
thats kind of what I was thinking. Does anyone know how the vacuum pump is connected to the engine or is it separated by some kind of valve? I thought it might be a one way valve from brake booster to engine/vacuum pump (if there is one) and its pulling vacuum from engine simulating a vacuum leak. or if I disconnect the vacuum pump or unplug it, will it set a code. I thought it might be a way to rule out pump and or the booster if I can isolate them.

Thanks for the replies.
 
#15 ·
Brie94 said:
Hi Everyone!
I have a 2018 Jeep Grand Cherokee Limited. It's the 4WD 3.6L and there are NO CODES. I have a slightly rough idle when in park and while stopped with my foot on the break. One weird thing I noticed is the harder I press my foot on the break, the more I feel that vibration (RPM'S also slightly drop which I am unsure if this is normal). I replaced a vacuum hose that commonly breaks on these and also tried the trick to reset the throttle position sensor. Rough idle still remains....my next steps are to replace the air filter, fuel filter, clean the throttle body and try fuel injector cleaner. I'm really at a loss being there are no codes and the car runs and shifts as normal once I am driving. This has been going on for almost a month...I was hoping it would throw a code to help diagnose the issue but I guess it wants me to struggle...jeep life lol. Has anyone else experienced this issue? If so what was the problem? Any tips, advice and ideas are appreciated!
Click to expand...
I have the same issue with my 2018 Jeep Chetokee Laredo. Had a shop hook-up their diagnostic sensor, they came back and said it's either Cylinder #6 or the Spark Plug. Spoke to another shop, they said it might be the ignition coil. Did you ever find out what the issue was with yours?
 
#16 ·
Brie94 said:
Hi Everyone!
I have a 2018 Jeep Grand Cherokee Limited. It's the 4WD 3.6L and there are NO CODES. I have a slightly rough idle when in park and while stopped with my foot on the break. One weird thing I noticed is the harder I press my foot on the break, the more I feel that vibration (RPM'S also slightly drop which I am unsure if this is normal). I replaced a vacuum hose that commonly breaks on these and also tried the trick to reset the throttle position sensor. Rough idle still remains....my next steps are to replace the air filter, fuel filter, clean the throttle body and try fuel injector cleaner. I'm really at a loss being there are no codes and the car runs and shifts as normal once I am driving. This has been going on for almost a month...I was hoping it would throw a code to help diagnose the issue but I guess it wants me to struggle...jeep life lol. Has anyone else experienced this issue? If so what was the problem? Any tips, advice and ideas are appreciated!
Click to expand...
Hi there! I have a the exact issue with my Jeep Grand Cherokee and was wondering if you were able to find the cause of the problem. Any insights or advice would be really appreciated. Thanks!
 
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TonkaGA
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