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muddeprived
07-18-2009, 09:42 AM
Help me out guys so I know where to start lookin.

When I start up the jeep for the first time in the morning it would start up just fine but rumble and shake back and forth for about 6-8 seconds then it idles out fine. The rpms are normal during this time. It's just a rough rocking-type shake. It only happens right after you start it up, almost like there's no oil and it's trying to run dry and something like a motor mount broke and the motor shaking loose. hard to explain but has anyone had this issue? Over the past couple of months I've noticed the idle at a stop sign or stop light has a very slight rumble every couple seconds too. It might be related. It only does this during the very first start after sitting for 1/2 day or so.


Thanks

AJ99
07-18-2009, 10:26 AM
one of my buddies called me last night and his jeep just started this too? His is an 01. I am not sure what it is he says his does it for a few seconds and then his oil pressure goes up and it is fine after a few seconds of it...

muddeprived
07-18-2009, 10:48 AM
one of my buddies called me last night and his jeep just started this too? His is an 01. I am not sure what it is he says his does it for a few seconds and then his oil pressure goes up and it is fine after a few seconds of it...

Mine's an 01 too. It does it right after you start up and then once the pressure hits around 40 it stops and idles like normal. It only does it for only a few seconds.

BlueXJ
07-18-2009, 12:07 PM
Try cleaning the IAC to see if there is carbon buildup. Let us know what you find mudd.

Melissa
07-18-2009, 02:07 PM
I've noticed the idle at a stop sign or stop light has a very slight rumble every couple seconds too. It might be related.
Thanks

My 93 does this at an idle too, but mine does not do the other when I start it up.

muddeprived
07-18-2009, 02:33 PM
Try cleaning the IAC to see if there is carbon buildup. Let us know what you find mudd.

I will try this tomorrow. I just noticed that it's starting to shake when stopped, almost all the time now. Something's going.....

muddeprived
07-19-2009, 07:52 AM
Try cleaning the IAC to see if there is carbon buildup. Let us know what you find mudd.


Here's my IAC:

http://i37.photobucket.com/albums/e73/muddeprived/cherokee/idle%20fix/PIC-0079.jpg

http://i37.photobucket.com/albums/e73/muddeprived/cherokee/idle%20fix/PIC-0080.jpg

What's a good way to clean that tip? Do you think it's bad enough to cause my idle issue?

Mudderoy
07-19-2009, 11:48 AM
Here's my IAC:

http://i37.photobucket.com/albums/e73/muddeprived/cherokee/idle%20fix/PIC-0079.jpg

http://i37.photobucket.com/albums/e73/muddeprived/cherokee/idle%20fix/PIC-0080.jpg

What's a good way to clean that tip? Do you think it's bad enough to cause my idle issue?

That reminds me. I cleaned my throttle body a few months back, and this thing was flithy, as was the throttle body. I used throttle body cleaner, and I suspect that would be fine on the IAC as well.

AJ99
07-19-2009, 01:46 PM
well did that fix the rough idle.

muddeprived
07-23-2009, 08:15 AM
Nope. :cool:

btfury
07-24-2009, 02:16 PM
my 2000 is doing the same thing. I've got a buddy who's a mechanic and I asked him and he mentioned that it might be the fuel pump, fuel pressure check valve, leaky fuel injector or CPS. thought I would throw that out there

Victoriabcboy
10-24-2012, 12:18 AM
I know this is and old thread but has anyone come up with an answer to this problem?? I've got a '99 and it does this shake rough idle after start up. Sounds like the same symtoms.

Just checking to see if anyone has had any luck solving this or if it's just a jeep trait?

4.3LXJ
10-24-2012, 12:53 AM
Chris finally solved this problem. It was the infamous heat soak on his vaporizing gas in the injectors. The way he solved it was to use a fan timer, a complicated install that I helped him with, that used the efan to blow air on the injector area for ten minutes I believe. He has to have a god battery for this. But he says it took care of it. He does however live in Penn. So not sure how hot the weather is there.

Victoriabcboy
10-25-2012, 12:47 AM
So he had gas vaporizing in/before the injectors? Due to heat in the fuel rail area?

I don't think that's going to be my problem, mine is after start it rough idles to what seems like it's going to stall then it's fine till the next start after sitting for some time. Plus the motor is bone cold.

Guess I'm going to have to start the good old shotgun aproach, check and or replace one part at a time lol.

Cheromaniac
10-25-2012, 04:38 AM
There are TSB's for the rough idle after cold start, long crank times, and for the injector heat soak issues:

http://www.wjjeeps.com/tsb.htm

4.3LXJ
10-25-2012, 06:28 AM
So he had gas vaporizing in/before the injectors? Due to heat in the fuel rail area?

I don't think that's going to be my problem, mine is after start it rough idles to what seems like it's going to stall then it's fine till the next start after sitting for some time. Plus the motor is bone cold.

Guess I'm going to have to start the good old shotgun aproach, check and or replace one part at a time lol.

You might start with some Sea Foam in the gas and check fuel pressure on start up. The Sea Foam is a good thing to do anyway and the fuel pressure on start up is a good idea. One thing that happens is the check valve in the tank doesn't hold pressure and then doesn't get back up to pressure on that two second fuel pump activity. I think Mudderoy had a similar issue and had to replace the sending unit in the tank to fix it.

Victoriabcboy
10-28-2012, 10:25 AM
good idea on where to start thanks