Rough idle, pulled #4 spark plug no change?

disaster06

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So I bought my buddies 89 2.5L YJ and he said it had a rough idle from just getting the vapor lines replaced recently. Said it didn’t do that before, it only is rough when it’s cold though, it will idle at 500 rpm, then after about 5 mins, picks up to about 800-900rpm and really smoothes out. When it was rough, a friend pulled the spark plug wires and each one caused a stumble except #4. There was almost no change at all. It does stumble however after it’s warmed up. Any ideas on what would cause it to have these issues only when cold?

Nick
 

Stoopid Jeep

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Pull the plug and look at it. In fact, pull them all and look at them
Look inside the distributor cap make sure everything looks good in there. Inspect/test the plug wires.
After that, a spark test and a compression test ate probably in order.
 
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disaster06

disaster06

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I replaced plugs with Bosch plugs when I did a tube up along with plug wires, new cap and rotor, changed oil and filter and air filter. They all looked ok. Cylinder 2 looked sooty but was dry. These are in order from front to
F38368DA-49EC-49B6-A516-6619CCAC4AB0.jpeg
back as they sit, right being the front of the engine block. Inside of cap and rotor looked fine as well
 

Stoopid Jeep

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I replaced plugs with Bosch plugs when I did a tube up along with plug wires, new cap and rotor, changed oil and filter and air filter. They all looked ok. Cylinder 2 looked sooty but was dry. These are in order from front to View attachment 120146back as they sit, right being the front of the engine block. Inside of cap and rotor looked fine as well
That's weird, number 4 sure looks like it was burning just about perfect.
You might pop the new plugs our and look at them (just to see if they're stll ok)

Double check firing order?

I would quadruple check every vacuum line.
 
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disaster06

disaster06

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Yea, pulling the plugs is next to see if there is any oil or gas on the plugs. Just weird that it stabilizes out after it comes up to maybe 150 degrees or so. Wasn’t sure if any sensors had to “heat up” before things opened or closed and started working differently when warmed up as opposed to cold.

Side note, the smog shop that replaced vent lines said a vent line to the EGR was pinched but they didn’t fix anything, it still idles rough at cold. Might have just made it up to shut me up
 

Gilaguy23

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A leaky egr valve will make it idle like sheeeeettt. The seat gets burnt like a bad valve. You might try replacing it and see what that does. next I see Champion plugs but you said Bosch. IMO if you have Bosck plugs in there,platinums or?? , throw them in the shit can and go back to plain old champions. #3 is obviously way to rich, are you sure you did not crack the porcelin putting the new ones in?
 
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disaster06

disaster06

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I put in platinums, pre-gapped. Bosch isn’t good? I’ve always thought of them as a top tier. I was super careful putting in the plugs and torqued them to the correct spec with a torque wrench. It was idling like this when I got it. I was just hoping to fix it with a tube up
 
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disaster06

disaster06

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And when you say the seat gets burnt, are you talking about the gasket? I found those for like $3. A new EGR is like $80 for some reason. Damn 4 cylinder! I was also thinking maybe the idle air control valve could be dirty?
 
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disaster06

disaster06

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And when you say the seat gets burnt, are you talking about the gasket? I found those for like $3. A new EGR is like $80 for some reason. Damn 4 cylinder! I was also thinking maybe the idle air control valve could be dirty?
Nevermind, I just saw a video about cleaning the EGR and how to test if it is functioning. Totally understand what you mean about the seat now
 

Gilaguy23

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For whatever reason most guys who drop in high dollar plugs with the hopes of better mileage or?? find soon after CEL and bad running/economy. Seems Bosch heat ranges are out of wack or something, I also say this first hand after installing them in a 4x4 suburban and a then new Jeep XJ. Mileage and performance when to shit. Its pretty common at the TJ forum to find a few posts a week regarding this issue. Best fix is to install basic Champion OEM style plugs. if your bored google "why dont bosch plugs work in jeeps" lost of reads on the subject.
 
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disaster06

disaster06

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I found a vacuum line not connected on top of my throttle body. I think they go to the TAC sensor from what I have googled, but don’t know where that is located? One line goes into the airbox, the other line is just dangling. Is the TAC sensor also in the airbox?
 

Flyer58

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You'll find several factory service manuals in the resources section of this website which will help you. Free for the download.