4.0 running rough

[Scal]

I have a 1998 Jeep Wrangler Sahara 4.0L. A couple months ago I upgraded the ignition system(new coil, rotor, cap, plug wires and plugs) because it was idling rough. Well, its been in now for a few months and its a little better but still on the rough side. The best way to describe how the idle sounds is that every couple seconds or so you can hear a "pop" or too from the tail pipe(when standing behind it). Its worse on initial startup and gets less noticable and less frequent when the engine is warm. The distributor is the only thing i did not change so maybe its due? I cant seem to narrow it down to what it could be. I know a rough idle could be a sign that the engine had overheated somtime in its past but the guy i bought it from said he never had any problems. Anybody have any ideas?

 

[Quest]

Without knowing the history of your vehicle, we can only make guesses...

check the following:

1)ignition timing
2)check for CEL codes
3) check for clogged/cat core meltdown which makes the exhaust restrictive
4)check to see if your EFI system is running overly rich
5)check for air leaks on the intake/exhaust end, inc. intake manifold and all the joints, exhaust manifold and all the exhaust pipings, etc.
6)try a can of FIC.

 

[chrome]

Also check your valve clearance, too tight a clearance can lead to a rough idle. Happened to me when I tightened up the clearance on a 4 cyl. Mitsubishi engine to try and eliminate valvetrain noise, it developed a rough idle. Loosened up the clearances to spec, and the rough idle went away.

 

[Greaser]

What type of plugs did you install?

 

[HardbodyLoyalist]

"What type of plugs did you install?"

And what was the gap?

 

[Scal]

I put in Champion Truck Plugs because of the praise they get on my jeep forum. The gap is set to .040 even though the factory recomends .035. I did this because with my upgraded ignition i should be able to run up to a .065 gap. There is a tech right up on the web of a guy who put the same thing in his jeep with no trouble running the bigger gap. So i tend not to thnink or hope its not anything to do with my ignition system. Its not throwing any codes. Could this be from carbon buildup? I guess what im going to have to do is try a multitude of different things until it goes away. Only thing is that im at college and my jeep is at home in the garage. Anything you guys can suggest would be great, ill try everything until it goes away. Thanks for all the help so far,
-Ryan

 

[Gary Allan]

Try some mechanic in a can injector cleaner. I've had good results with Gumout Regane ...but I've switched my brand loyalty lately (wink:wink).

If you had intake manifold leaks ..your idle would be high. Happens all the time when someone has to work on the exhaust manifold.

Clean you throttle body and the AIS.

Valve lash is not adjustable on this engine.

If you want something to do, pull the cap and see how much slack is in the timing chain. Just see how many degrees of crank rotation is required to move the rotor when you stop it in one direction. I think 12 degrees is the limit (that failing memory).

Your odometer display should show any pending codes with the key technique (ON-OFF-ON-OFF-ON-leave on) ..or it may be the CEL flashes. If it's the CEL flashing, it will deliver a series of two digit codes. Flash-Flash-Flash (pause) Flash-Flash would be 32. There's a longer pause between the two digit flash streams. They are always two digit.

allpar codes for 80's through 90's stuff

 

[Scal]

awesome, thanks guys...ill try some of these.

 

[mechtech2]

It could be simply an injector that is dirty, making it mismatched to the others.
Chevron Techron, Gumout Regane, or Redline S1 are proven cleaners. You may have carbon on the valves, acting like sponges and screwing up your idle - these cleaners will also attentuate that.
ALL of you vacuum lines and connections have to be perfect - you'll have to visually and manually check each one.
A compression check would tell you if a cyl is laying down on you.