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Rough idle following spark plug change

9K views 13 replies 6 participants last post by  That phucker 
#1 · (Edited)
My 2008 Patriot WAS running great, but due to a drop in gas mileage from 19+ to 17mpg City driving, then discovering the plugs were suppose to be changed at 30k (I have 40k)..........I decided to change the spark plugs.

Replaced with original OEM NGK (ZFR5F-11)plugs, used antiseize and Dielectric on plugs. My gas mileage is no better and now my engine idles rough, it idles like the AC is on but it is not.

I made sure the gap was per owners manual .44.

Advise welcome!:
 
#2 ·
Mine never idled rough on the very rare occasion I used dash controls instead of a window crank for AC. It ran rough when I switched out for Champion double-platinum plugs, but once they were properly gapped(which I thought I remembered was .41, not .44), it ran fine.

Also, engine would sound different if an O2 sensor was bad, but then your check engine light would be on. Maybe air filter is getting dirty?
 
#3 ·
Your fuel economy sounds rather low to start with. Regardless, if the problem started after changing the plugs, I'd bet on a bad plug or loose connection.
Be sure all the connections are secure.
If so, try disconnecting one at a time so see if you can isolate the problem to a particular cylinder.
Presuming you can, maybe you have a bad plug or a bad coil. At 9 years old, it could be a bad coil, though mine are still OK. (Don't jinx me!)

FYI, OEM plugs should come pre-gapped and if you messed with them that could be the problem.
From what I've read on other posts, .44 seems to be right, but there is conflicting info out there. DO you have a decal under the hood? Have you checked the owners manual?
Here's a thread I just checked: http://www.jeeppatriot.com/forum/15-engine-drivetrain/14385-spark-plug-gap-question.html

Oh, I just realized this is your first post. Welcome to the forum!
Use the search window at the top right of this page and see what else you can find.
 
#5 ·
one of the leads/packs will be bad

your moving the leads has done something

...pull one lead only at a time and if there is no change in idling with one lead, then you have found problem. if each time you pull a lead, the engine gets worse then the problem is elsewhere
 
#6 ·
Hi.
Welcome.
Is there a chance that you got some anti-seize compound on the porcelain insulators?
If so, that can cause a mis-fire. Anti-seize compound in an EXCELLENT conductor of high-voltage electricity....
As already mentioned, check your connections.
Did you have your battery disconnected while changing plugs?
 
#10 ·
As long as you didn't have anti seize all over your fingers while handling the plugs, you should be okay that way.

I generally disconnect the battery while doing the plugs and air filter. This allows the ECM to re-learn it's fuel trim mapping based on the new plugs. It gives me an opportunity to clean the battery terminals, too.
Your idle might be even worse after doing that but it should correct itself in short order.
 
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