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Unread 10-25-2013, 01:08 AM   #1
WantMoreOUTDRS
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1998 XJ Cherokee 
 
Join Date: Sep 2012
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Rough idle and terrible gas mileage (worse than before)

#1 Thank you for your time #2 I searched the site for topics with "rough idle" and got great info. just thought it wouldn't hurt to explain my specific case. #3 I appreciate any, simple or complex, advice anyone will give me. I'm getting into working on my jeep, but im no full on mechanic...

'98 XJ I6 4.0L
192,000 miles

Rough idle the whole time I'm driving. usually dips down to about 600 rpm's when breaking. also makes a jump up from the rough idle to about 1000 rpm's every 2 mins or so. I've recently had the fuel injectors flushed. I pulled out the spark plugs, one of them was bent a bit. So i bent it back, cleaned them all with a bit of gas. the cleaning (and the flushing injectors) helped the problem for about 3 days... then back to rough. ive seafoamed her about 10k miles ago. i added the seafoam thru the brake booster, only. seafoam her again? thru the oil, gas tank, and vacuum hose? i guess ill ask my mechanic to run a compression test? (feedback?)

she doesnt over heat. stays at 210. there are some tiny bubbles coming up in the coolant.

like i said. thank you for your time and just want some help, not to get bashed for making a repeated thread or anything. thanks again.


Last edited by WantMoreOUTDRS; 10-25-2013 at 01:22 AM..
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Unread 10-25-2013, 07:02 AM   #2
Azzy
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Bent it back? Did you properly gap it, or just "bend it"?
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Unread 10-26-2013, 09:40 AM   #3
WantMoreOUTDRS
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bent... so now that you said that, i replaced all of them with champion spark plugs. still have terrible gas mileage. someone mentioned to me the ERG valve?
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Unread 10-26-2013, 12:58 PM   #4
xjdantheman
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Quote:
Originally Posted by WantMoreOUTDRS View Post
bent... so now that you said that, i replaced all of them with champion spark plugs. still have terrible gas mileage. someone mentioned to me the ERG valve?
Fuel pressure regulator is my guess. Diaphragm inside is probably leaking gas into the vacuum line. I had on old bmw that ran rich, idled bad and bad mpg, the fps was the issue.
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Unread 10-26-2013, 02:11 PM   #5
habbyguy
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Could be an exhaust leak messing with the O2 sensor (and therefore the computer that sets the fuel injection scheme). Or just a bad O2 sensor (if it's never been replaced, it's loooooong overdue). With the price of gas, it can't hurt to just replace the O2 sensor "just in case"... it'll likely pay for itself in short order even if it wasn't "bad".
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Unread 10-28-2013, 07:36 AM   #6
Azzy
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Have you checked your fuel pressure?
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Unread 10-29-2013, 12:56 PM   #7
WantMoreOUTDRS
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my fuel guage has given wrong reads acouple time. saying theres no gas when i know there is. im guessing this supports the idea that the fuel pressure guage is bad and needs replacing?
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