# Jeep engine help -- Paging Rick!
**URL:** https://boards.straightdope.com/t/jeep-engine-help-paging-rick/539354
**Category:** Factual Questions
**Created:** [May 13, 2010, 10:16pm UTC](https://boards.straightdope.com/t/jeep-engine-help-paging-rick/539354 "2010-05-13T22:16:50Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)
#### Post date: [May 13, 2010, 10:16pm UTC](https://boards.straightdope.com/t/jeep-engine-help-paging-rick/539354/1 "2010-05-13T22:16:50Z")
A friend of mine has a Jeep Wrangler (I don’t know what year) with a 4.0l six. She says it’s running a little rough.
> [@friend](#):
>
> The Jeep went in for a tune up while I was off that week, still has this rough running feeling that no one can seem to pinpoint. [Mechanic] says it’s a vacuum leak somewhere but every time I take it to him to fix he can’t find it or just doesn’t know where to start looking for it. It’s been doing this for over a year now, it runs fine besides that and even better when the weather is warmer so I’m not taking it in until it turns into a problem.
>
> \<2nd email\>
>
> The Jeep is vibrating really bad, feels like it’s coming from underneath. Could be the throttle body. [Mechanic] did mention that, might be a hole in the exhaust pipe too. Yes, the manifold is cracked but it has been for a while, way before this rumbling occured. [_NB: The exhaust manifold on Jeep 4.0l engines tend to develop cracks. – J L.A._] I don’t ever drive on the freeway anymore so I don’t know if it needs to be blown out so to speak. I do know that it runs a little smoother in warm weather and that you only feel it when you’re at a stand still with the engine running.
>
> [Mechanic] said it could be the engine mounts too. I just had a transmission mount replaced, and older cars tend to loosen up with age and vibrate a lot more. Not really sure exaclty what’s causing it but it’s running fine other than this issue.
**Rick** and other automotive Dopers, any guesses as to the source of the problem?
---
### Author:  [@Fubaya](https://boards.straightdope.com/u/Fubaya)
#### Post date: [May 14, 2010, 3:05am UTC](https://boards.straightdope.com/t/jeep-engine-help-paging-rick/539354/2 "2010-05-14T03:05:57Z")
No idea about the rough running feeling, but what did she replace the transmission mount with? I replaced my factory mount, which is pretty soft, with a heavy duty poly mount that vibrated like crazy.
Does she have factory tires/suspension? A little suspension lift can put the driveline in a bind and cause vibrations when stopped and/or just as it starts moving.
---
### Author:  [@Gary\_T](https://boards.straightdope.com/u/Gary_T)
#### Post date: [May 14, 2010, 4:18am UTC](https://boards.straightdope.com/t/jeep-engine-help-paging-rick/539354/3 "2010-05-14T04:18:26Z")
I gather the symptom is strictly a rough idle, with the engine running well otherwise.
Checking for obvious vacuum leaks is a good place to start. Next thing to check is carbon build-up in the throttle body. Not much point in going any further until those two areas are known to be in good shape.
---
### Author:  [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)
#### Post date: [May 14, 2010, 3:01pm UTC](https://boards.straightdope.com/t/jeep-engine-help-paging-rick/539354/4 "2010-05-14T15:01:58Z")
> [@Fubaya](#):
>
> Does she have factory tires/suspension? A little suspension lift can put the driveline in a bind and cause vibrations when stopped and/or just as it starts moving.
It’s been a while since I’ve seen her in person, but I think it might be raised a little. Maybe just the factory ‘up-country’ option. (She bought it used.) Wouldn’t vibrations caused by the suspension have cropped up earlier?
> [@Gary\_T](#):
>
> I gather the symptom is strictly a rough idle, with the engine running well otherwise.
>
> Checking for obvious vacuum leaks is a good place to start. Next thing to check is carbon build-up in the throttle body. Not much point in going any further until those two areas are known to be in good shape.
Her mechanic friend thinks it’s a vacuum leak, but couldn’t find one. I hadn’t thought about the throttle body.