Did tune up on 4.0 ZJ... now it runs rough at idle.

[candymancan]

Did a tune up like ive done 20 times prior new cap rotor. Plugs. Wires. And the Jeep runs rough at idle now backfored a few times. I checked my wiring and i aparently the disgrams online were wrong. And 2 wires were wrong.

Put the wires on correcntly and now its rough at idle. Sounds odd out the tailpipe and it wont stay idle it wants to surge up and down a little.

So i took the plugs out and checked them. Put them back in. And then it idled just fine. Drove fine. But then my mom said on her way home today it was rough idling at stops. So it came back.

The distributor cap is the older one. I thougjt the new one was doing it. The rotor is new though.

The old plugs were champions. Severly worn out though gapped to like .50 from wearing out. The new plugs are autolights. Ive actually never used autolight before.

Im starting to wonder. After pulling the plugs and reseating them it ran fine. Now its doing it again.. could it be these autolight plugs ? Im debating on fishing the old plugs outa the trash. Regapping them to .35 even thpugh the diode is worn down badly. And see if it still does this.

Im suspecting its the plugs or new wires.


Doing google searchs im finding similar problems with other people after a tune up. So what do you guys think ? Is it the new plugs.

[Stuka]

Do you have a scan tool? (If not, the blue tooth ones that hook up to your phone are great).

Being able to scan and see what the computer is trying to do would likely aid in figuring out the issue.

Were the new plugs the same temperature as the old ones? Though its unlikely this would cause what you are seeing. Normally if there is a spark plug issue, it starts to happen at higher throttle when there is more fuel in the cylinder. If its bad at idle due to plugs, its typically undrivable under load.

If the issue is primarily at idle, I am not sure its spark related. To me it sounds like a sticking IAC (Idle Air Control Valve). The primary symptom of a bad IAC valve is stalling at idle, or an idle that hunts arounds up and down.

This valve failed on my Wife's XJ. And until we could get a new one, I simply unplugged it. It stopped the stalling and idle hunting. Though it also made it harder to drive. But it was a good test to see if it was the cause.

[candymancan]

985 autolights.. i returned them got champion rc12lyc. Like i should have.. now it runs fine.

Sorry for wasting space on the forum. Ive heard autolights suck before for these engines.. but now ive personally experienced it

[Stuka]

985 autolights.. i returned them got champion rc12lyc. Like i should have.. now it runs fine.

Sorry for wasting space on the forum. Ive heard autolights suck before for these engines.. but now ive personally experienced it

Makes me wonder if one of them was just defective.

I ran that plug in my 258 and my 4.0, never had an issue. But at least its working well for you now.

[sierrablue]

Honestly I'm surprised that the Champions work at all...our family has never had any luck with them.

The copper core Autolites we've had really good luck with. They don't last since they're copper but they give you a good spark.

[candymancan]

Lol the champions lasted 40k miles at least.. look how worn they were though.

[sierrablue]

Dang!

On my grandpa's '50 Buick he did Champion plugs once and it wouldn't idle right, no matter what he did. Put a set of Delcos in and it ran perfect.