Rough idle
08-23-2011, 09:35 AM
#1
CF Veteran
Thread Starter
Join Date: Oct 2010
Location: Salem Nh
Posts: 1,756
Likes: 0
Received 1 Like
on
1 Post
Year: 1998
Model: Cherokee
Engine: 4.0
My rig has a slight rough idle, things that I have changed are plugs, wires, cap, rotor, oil, filter, air filter, and I.just put in some 703's, I feel like they did rlly nothing to help. It has a.slight knock when cold thinking itd a lifter cause it sounds like its coming from the top of the engine but its always had a slight knock, once up to temp its almost gone also it idles a bit better once up to temp. It drive fine with no problems and is throwing no codes. Any ideas? Also im running pennzoil high mileage do u think I should switch to something else?
Last edited by jeepxj19; 08-23-2011 at 10:01 AM.
08-23-2011, 07:48 PM
#5
CF Veteran
Join Date: Jun 2011
Location: Nor-Cal
Posts: 2,858
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1990
Model: Cherokee
Engine: The venerable 4.0
Do 703s have removable pintle caps? If so one could have gotten cocked on installation. This happened once with my 5.0 injectors. Same symptoms.
08-23-2011, 08:53 PM
#6
Member
Join Date: Aug 2011
Posts: 103
Likes: 0
Received 0 Likes
on
0 Posts
Model: Cherokee
idle...
Cap, rotor, plugs, wires...wont make a bit of difference if the throttle body is all gunked up. 10, 15, 20 yrs of carbon and gunk will make all that brand new stuff useless. Clean your throttle body, whenevery you tune it up....good practice, and wont hurt a thing....But just my 2 clams...
08-23-2011, 08:58 PM
#7
Seasoned Member
Join Date: Jun 2011
Location: Catasauqua PA
Posts: 287
Likes: 0
Received 1 Like
on
1 Post
Year: 1996
Model: Cherokee
Engine: 4.0
Originally Posted by jeepxj19
My rig has a slight rough idle, things that I have changed are plugs, wires, cap, rotor, oil, filter, air filter, and I.just put in some 703's, I feel like they did rlly nothing to help. It has a.slight knock when cold thinking itd a lifter cause it sounds like its coming from the top of the engine but its always had a slight knock, once up to temp its almost gone also it idles a bit better once up to temp. It drive fine with no problems and is throwing no codes. Any ideas? Also im running pennzoil high mileage do u think I should switch to something else?
1. Confirm fuel pressure. You should have 49 psi at the rail. If it's not, check the fuel pump.
2. Since you changed everything else in the secondary ignition system, change your ignition coil. Costs about $35 and takes 5 mins.
3. Seafoam, seafoam, seafoam. Get the spray can with the long red tube. Follow the directions on the can, enjoy the smoke. Get a can of the liquid, pour a third in your gas tank, a third in the crank case and then pull off your brake booster hose and suck the rest of it through there. Again, enjoy the smoke.
3. Only use champion copper plugs gapped at .035.
4. Change the fuel filter. A dirty fuel filter will impede flow.
5. When you change your oil next, do an engine flush. I did this with mine, the old oil came out as black as Satans heart. It was so bad I did it twice, then dropped the oil pan and cleaned it out. Some of it was like curdled milk.
6. Clean the IAC. There's technical write ups on the forum that will explain how to do it. While you're at it, clean the throttle body.
7. Check for vacuum leaks. Refer to write ups.
8. Clean every ground in the engine bay you can find...polish 'em and put 'em back on. Start with the strap near the back of the valve cover that's attached to the firewall on the drivers side, then the one on the dipstick tube bolt.
Theres like 100 things that will cause a rough idle, but that's all I can think of, if none of that works, good luck!!
Trending Topics
08-24-2011, 06:31 AM
#8
CF Veteran
Thread Starter
Join Date: Oct 2010
Location: Salem Nh
Posts: 1,756
Likes: 0
Received 1 Like
on
1 Post
Year: 1998
Model: Cherokee
Engine: 4.0
Originally Posted by CattyXJ
I've been fighting the rough idle for months, and I finally got it beat. You're on the right track with the things you did, but try the following:
1. Confirm fuel pressure. You should have 49 psi at the rail. If it's not, check the fuel pump.
2. Since you changed everything else in the secondary ignition system, change your ignition coil. Costs about $35 and takes 5 mins.
3. Seafoam, seafoam, seafoam. Get the spray can with the long red tube. Follow the directions on the can, enjoy the smoke. Get a can of the liquid, pour a third in your gas tank, a third in the crank case and then pull off your brake booster hose and suck the rest of it through there. Again, enjoy the smoke.
3. Only use champion copper plugs gapped at .035.
4. Change the fuel filter. A dirty fuel filter will impede flow.
5. When you change your oil next, do an engine flush. I did this with mine, the old oil came out as black as Satans heart. It was so bad I did it twice, then dropped the oil pan and cleaned it out. Some of it was like curdled milk.
6. Clean the IAC. There's technical write ups on the forum that will explain how to do it. While you're at it, clean the throttle body.
7. Check for vacuum leaks. Refer to write ups.
8. Clean every ground in the engine bay you can find...polish 'em and put 'em back on. Start with the strap near the back of the valve cover that's attached to the firewall on the drivers side, then the one on the dipstick tube bolt.
Theres like 100 things that will cause a rough idle, but that's all I can think of, if none of that works, good luck!!
08-24-2011, 06:42 AM
#9
Seasoned Member
Join Date: Jun 2011
Location: Catasauqua PA
Posts: 287
Likes: 0
Received 1 Like
on
1 Post
Year: 1996
Model: Cherokee
Engine: 4.0
Originally Posted by jeepxj19
I havnt checked the fuel pressure yet, I just seafoamed it a couple days ago it didn't change anything. I have already cleaned the throttle body and IAC ( I made the write up), do I have to drop the tank to get to the fuel filter? And I have no apparent vacuum leaks.
08-24-2011, 07:31 AM
#10
CF Veteran
Thread Starter
Join Date: Oct 2010
Location: Salem Nh
Posts: 1,756
Likes: 0
Received 1 Like
on
1 Post
Year: 1998
Model: Cherokee
Engine: 4.0
do u think replacing the cps or replacing the IAC would clear anything up? again i cleaned the IAC and the throttle body a few months ago, so im assuming that should be fine. any insight on the cps?
08-24-2011, 07:46 AM
#11
Seasoned Member
Join Date: Jun 2011
Location: Catasauqua PA
Posts: 287
Likes: 0
Received 1 Like
on
1 Post
Year: 1996
Model: Cherokee
Engine: 4.0
Originally Posted by jeepxj19
do u think replacing the cps or replacing the IAC would clear anything up? again i cleaned the IAC and the throttle body a few months ago, so im assuming that should be fine. any insight on the cps?
08-24-2011, 08:21 AM
#13
Seasoned Member
Join Date: Jun 2011
Location: Catasauqua PA
Posts: 287
Likes: 0
Received 1 Like
on
1 Post
Year: 1996
Model: Cherokee
Engine: 4.0
Originally Posted by jeepxj19
I kno that a cps is a issue for xjs, but i really dont want to spend the $ if it turns out not to be the issue
08-24-2011, 08:28 AM
#14
CF Veteran
Thread Starter
Join Date: Oct 2010
Location: Salem Nh
Posts: 1,756
Likes: 0
Received 1 Like
on
1 Post
Year: 1998
Model: Cherokee
Engine: 4.0
Well i have been told that one on its way out could cause misfire and rough idle, but then i have also read that a cps does slowly fail, it either works or doesnt. so idk.
08-24-2011, 08:33 AM
#15
Seasoned Member
Join Date: Jun 2011
Location: Catasauqua PA
Posts: 287
Likes: 0
Received 1 Like
on
1 Post
Year: 1996
Model: Cherokee
Engine: 4.0
Originally Posted by jeepxj19
Well i have been told that one on its way out could cause misfire and rough idle, but then i have also read that a cps does slowly fail, it either works or doesnt. so idk.