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  #1  
Old August 3rd, 2017, 10:37
jayo310 jayo310 is offline
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99 XJ Engine Vibration only in Neutral/Park on Cold Start!!!

Hey guys! This is my first post and I need some help. I bought my car a month ago knowing it needed work. But this is one thing I can't figure out, any suggestions are welcome!

I'm getting some weird vibrations with my engine that's shaking my whole car, not a violent shake but very noticeable. The vibration is very rhythmic and the exhaust follows the rhythm. It's almost like a put put of a old choo-choo train. It only occurs on a cold start, and not so noticeable in the beginning after I start the engine. But builds up, and the vibrations get stronger as the engine gets warmer. If I put the car into drive or reverse, it stops. If I put it back in to park or neutral, it comes back. If I drive for about 10 minutes down the street, put it back into park, its significantly less noticeable and almost non-existent. I could see my RPMs jump around a little, but its mostly hanging around 700-750. And it drives great! Maybe the gas mileage is a little bit on the crappy side, but it seems ok.

I've also have had a P0301 come on and off which may or may not be related. I'm going to switch #1 fuel injector with another one, and same with the spark plug as a first step to diagnose the misfire.

Things that I have replaced:
Spark plugs and wires
Distributor
Exhaust Manifold (still need to re-check torque of the bolts)
IAC sensor
MAP sensor
O2 sensors
Air filter
Muffler

Any help would be greatly appreciated!!!
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  #2  
Old August 3rd, 2017, 10:39
jayo310 jayo310 is offline
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Re: 99 XJ Engine Vibration only in Neutral/Park on Cold Start!!!

I forgot to mention...

1999 XJ 4wd 6 cyl Automatic transmission
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  #3  
Old August 3rd, 2017, 12:59
blakews2217 blakews2217 is offline
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99 XJ Engine Vibration only in Neutral/Park on Cold Start!!!

My thinking is as follows. Have you checked the motor mounts/ trans mount? Is it only when moving? Only when stopped? More noticeable when stopped vs going? By the chance of god a tweaked motor mount? Does it miss while going down the road?


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  #4  
Old August 3rd, 2017, 14:12
jayo310 jayo310 is offline
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Re: 99 XJ Engine Vibration only in Neutral/Park on Cold Start!!!

Thanks for your reply.

Have you checked the motor mounts/ trans mount?

Visually the motor mount looks ok. No signs of cracks or wear. They're rubber and I hear that oil can compromise the integrity. The engine is covered in some kind of oil or soot. I have not checked the trans mount yet, but will do that tonight.

Is it only when moving? Only when stopped? More noticeable when stopped vs going?

It's only noticeable only when it's stopped and worse when it's in park/neutral. It's also only bad when the car warms up from cold, before I drive it for a bit. After I drive it for a few minutes it gets much better. The temperature doesn't drop much lower than 65 here these days.

By the chance of god a tweaked motor mount? Does it miss while going down the road?

It doesn't miss going down the road. It has good power, and doesn't studder at all. I hope it's just a mount, but would that affect the "put put" of the exhaust?
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  #5  
Old August 3rd, 2017, 14:12
denverd1 denverd1 is offline
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Re: 99 XJ Engine Vibration only in Neutral/Park on Cold Start!!!

check mounts for sure

engine/trans damper would be another suspect area. inspection plate on bellhousing makes it really easy to check. Most XJ have these bolts loosen over time. If loose, add blue loctite and torque to spec
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Old August 3rd, 2017, 14:57
jayo310 jayo310 is offline
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Re: 99 XJ Engine Vibration only in Neutral/Park on Cold Start!!!

Sweet. Thanks for your suggestion. I will be checking it out tonight. I ran across this thread that has a fix for the problem I think you're suspect.

https://www.cherokeeforum.com/f51/ho...ocking-125547/

The Youtube video of his car sounds exactly like mine. I hope this is the answer to weeks of scratching my head.
https://redirect.viglink.com/?format=go&jsonp=vglnk_150179721065519&key=88d9c8a 0ab3ea24ba6250d4da7f8f93d&libId=j5wz0jtl010013qm00 0DAc6k0bmgw&loc=https%3A%2F%2Fwww.cherokeeforum.co m%2Ff51%2Fhow-fix-flexplate-knocking-125547%2F&v=1&out=http%3A%2F%2Fwww.youtube.com%2Fw atch%3Fv%3DPu7_jfDpeoU&ref=https%3A%2F%2Fwww.googl e.com%2F&title=How-to%20Fix%20Flexplate%20Knocking%20-%20Jeep%20Cherokee%20Forum&txt=Flexplate%20to%20To rque%20Converter%20Knocking%20%20%20%20%20%20-%20YouTube

I will keep you guys posted.
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  #7  
Old August 3rd, 2017, 17:04
blakews2217 blakews2217 is offline
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99 XJ Engine Vibration only in Neutral/Park on Cold Start!!!

Quote:
Originally Posted by jayo310 View Post
Sweet. Thanks for your suggestion. I will be checking it out tonight. I ran across this thread that has a fix for the problem I think you're suspect.

https://www.cherokeeforum.com/f51/ho...ocking-125547/

The Youtube video of his car sounds exactly like mine. I hope this is the answer to weeks of scratching my head.
https://redirect.viglink.com/?format...%20-%20YouTube

I will keep you guys posted.


I really know what it sounds like when the TQ decides it wants to back out. Sounds like a rod knocking HARD.


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  #8  
Old August 3rd, 2017, 18:40
jayo310 jayo310 is offline
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Re: 99 XJ Engine Vibration only in Neutral/Park on Cold Start!!!

Quote:
Originally Posted by denverd1 View Post
check mounts for sure

engine/trans damper would be another suspect area. inspection plate on bellhousing makes it really easy to check. Most XJ have these bolts loosen over time. If loose, add blue loctite and torque to spec
But do you these loose bolts would effect the jumpy RPMs and exhaust?

I'm going home and check on all the things you suggested.
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  #9  
Old August 6th, 2017, 09:47
Czjeeper Czjeeper is online now
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99 XJ Engine Vibration only in Neutral/Park on Cold Start!!!

If you have a p0301 code, that is a cylinder 1 misfire. Do a compression test. Are you losing any coolant?
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  #10  
Old September 12th, 2017, 14:15
jayo310 jayo310 is offline
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Re: 99 XJ Engine Vibration only in Neutral/Park on Cold Start!!!

*update*
Had the car checked out yesterday by a really good transmission specialist. He says that all diagnostic test resulted all look normal. The flex plate and bolts are good. There were two bolts in the valve body that were not torqued to spec, but nothing that would cause alarm. It might be that the transmission mount/engine mount might be a little worn. All wires and connections were checked and OK'd

The P0301 still shows up on the code reader but there is no CEL. One day it just disappeared but still stored. I can't feel any misfire while driving. Only sign of a misfire is an occasional long start.

The search continues....
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  #11  
Old September 13th, 2017, 05:23
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90xj06 90xj06 is offline
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Re: 99 XJ Engine Vibration only in Neutral/Park on Cold Start!!!

hows the rpm gauge look while idling? is it bouncing hard to 0 and back?

i had a grand Cherokee that had a loose crank sensor. it would misfire in park but when you put it in drive and the engine torqued a bit it was fine.
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