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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.
1998 Jeep Grand Cherokee 5.9L Limited 219k
1998 Jeep Grand Cherokee 4.0 I6 laredo 430k
1990 Jeep Grand Wagoneer 155k
1976 Jeep J10.. 85k(repaired)
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.