Rough Idle and missing at light throttle

robx251

robx251

Caught the Bug
I had an incident today and it kind of leaves me curious as to anyone else has had this issue and what they did to fix it. I have noticed a slight skipping while at idle at a stop light. Today it started to skip while driving with light throttle going down the road, so I figured that since I am at the 100k mark, I was due to to plugs and wires again as I last did them at 50k. after doing both new plugs and wires it hasn't gotten much better, I did throw in a bottle of the good fuel injector cleaner with this fill up at the time of new plugs, obviously too soon for a difference yet but just wondering if it might be a buildup on the throttle body as I have never cleaned that, or if I need to start looking for some other culprit.
 
Cleaning tbody not a bad idea. Also check for obvious vacuum leaks, etc. You could have even gotten a bad batch of fuel. Hard to go much further without a code.
 
WJCO said:
Cleaning tbody not a bad idea. Also check for obvious vacuum leaks, etc. You could have even gotten a bad batch of fuel. Hard to go much further without a code.
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I didn't see any vacuum leaks, I'll just do a cleaning tomorrow, it just stumps me only at light throttle
 
robx251 said:
I had an incident today and it kind of leaves me curious as to anyone else has had this issue and what they did to fix it. I have noticed a slight skipping while at idle at a stop light. Today it started to skip while driving with light throttle going down the road, so I figured that since I am at the 100k mark, I was due to to plugs and wires again as I last did them at 50k. after doing both new plugs and wires it hasn't gotten much better, I did throw in a bottle of the good fuel injector cleaner with this fill up at the time of new plugs, obviously too soon for a difference yet but just wondering if it might be a buildup on the throttle body as I have never cleaned that, or if I need to start looking for some other culprit.
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I had a bad coil that took awhile to trigger a code on a KJ. Your story sounds similar.
 
Get a scan tool that can monitor misfires and see if you can capture the cylinder that's misfiring.
Swap out that coil with one that's not having misfires and see if the misfire follows the coil. Simple :bleh:
 
So here is where I would start. You either have a bad coil, or a faulty injector. If you don't have any codes it would be hard to swap parts to see if it moves to another cyl.
 
Well, today I replaced the coil with a new one and did the Chrysler clean and beat top end cleaning. Still no luck. I did how ever finally get a coffee thrown. And I used my friends work scan tool who, new snap on touch screen. we found that it is a cylinder 1 misfire and only on light throttle and light to no load. we have come to the thinking that it is a leaking valve, most likely the intake side. we're next going to try the on engine valve job. He had done many of these and have been successful.
 
robx251 said:
Well, today I replaced the coil with a new one and did the Chrysler clean and beat top end cleaning. Still no luck. I did how ever finally get a coffee thrown. And I used my friends work scan tool who, new snap on touch screen. we found that it is a cylinder 1 misfire and only on light throttle and light to no load. we have come to the thinking that it is a leaking valve, most likely the intake side. we're next going to try the on engine valve job. He had done many of these and have been successful.
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Do a compression test and a cylinder leak down test before pulling things apart :spy:
 
Drdiesel1 said:
Do a compression test and a cylinder leak down test before pulling things apart :spy:
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Oh don't worry I did. When I did it the compression would fluctuate between 75 and 140. I am going to chock that up to not being able to get a real good seal with the tester. That I had. On a very good note, when I pulled the plug out to test this I looked it all over before putting it back in, I apparently hit the end when putting it in the first time, the gap was almost completely closed. I re-gapped the plug and I didn't notice a misfire yesterday after I put it back together.
 
Is it only once it gets warm? Check resistance of injectors. Could be multitude of things but start someplace and keep eliminating.
 
JeepinLife said:
Is it only once it gets warm? Check resistance of injectors. Could be multitude of things but start someplace and keep eliminating.
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No it wasn't only when warm. But it ended up being that when I put the new plugs in I must have tapped the end of the plug and closed the gap. After I re-gapped it after the compression test it is running normally again.
 
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