rough idle and miss during heavy acceleration - JeepForum.com

 
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post #1 of 2 Old 03-06-2013, 08:09 PM Thread Starter
Hrothgar
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2002 TJ Wrangler 
 
Join Date: Dec 2005
Location: Tigard, OR.
Posts: 245
rough idle and miss during heavy acceleration

Hi all,

Got a 93 5.2 zj limited, 174,000 miles with a rough idle/miss problem I've been trying to track down for a couple months. It sat for about ten months with a bad fuel sending unit.

In order of things I've recently done... New Crank Position Sensor (thought this was the orignal problem), New Fuel Sending unit and fuel filter (started right up).

Changed the oil and filter, removed and cleaned throttle body (looked for oil in plenum, didn't see any), and replaced IAC. Drove it like this for about a month until I could give it a tune up, which it desperatly needed even before the sending unit failed. BUT ran fine during that time. I say that again, it ran fine before tuneup.

Then the tuneup... changed plugs, wires, cap and rotor, and PCV valve. Thought someone was just being fancy with the convolute on the old wires, so I just put the new wires on sans convolute and went about my way. Came to regret that...

Didn't know about the TSB for plug wires on the 5.2 at the time, so of course it ran like crap immediately after. (rough idle, sputtering, poor acceleration) Searched for the issue and found the TSB, and performed all the steps in the TSB putting the old convolute on which was still in my trash can (whew!). Made it better, but still had issues. So I bought more convolute of a larger dia (3/8") and put it over the old stuff (which was 1/4"). Better again, but still not perfect.

Have also sea foamed it this weekend. Partially to hope it would help the rough idle, but mostly cause I've had been wanting to do it. Put 1/3 of bottle in gas, 1/3 in oil (was due for oil change again), and 1/3 down brake booster vaccum hose with jeep idling. Shut it off and let it sit for five minutes per instructions. started it back up and went for drive, but never got any smoke. Figured it was cause of the way I split the bottle, but still would have expected something.

So now, short of swapping yet another new cap and rotor or the old one back on, or another new set of wires or again trying to put the old set back on, I don't know what to try. I've check the firing order and I don't have any wires connected wrong. They are all seated properly on the cap and plugs. They are routed per the TSB, with 1 to 2 layers of convolute. Almost entire coil wire has two layers of convolute.

I know this is long, but if you made it this far, I would appreciate an opinion. Thanks!


'02 TJ 4.0 with some useless stuff bolted on.
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post #2 of 2 Old 03-07-2013, 10:32 AM
PolkaPower
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1998 ZJ 
 
Join Date: Aug 2011
Location: The Abyss
Posts: 19,301
Things that can cause a miss or rough idle. Bad gas, leaky injector, bad coil, 02 sensor, low fuel pressure, clogged cat, vacuum leak, bad PCM, ect. Then the stuff you said you fixed already. I probably left some things out.

Here is some reading to help you check things out. http://www.aa1car.com/library/misfire.htm
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