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Unread 08-03-2011, 08:36 PM   #1
rustyabiding
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1998 Cherokee 4.0 rough idle

Hi Im baffled by this problem. Im working on a friends 1998 Cherokee and it has a really rough idle but when you accelerate it runs just fine. I ran the codes and it says bank 1 misfire and bank 3 misfire. I replaced the TPS and the IAC because another jeep i worked on had a similar problem and that fixed it. Could it be something with fuel Pressure? Or what else could it be??
Thanks

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Unread 08-03-2011, 10:08 PM   #2
CJ7-Tim
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Are all the tune-up parts new or have less than 30,000 miles ? Used any fuel injector cleaner in the gas tank ? Tested the fuel injectors and inspected their wires ?
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Unread 08-03-2011, 10:13 PM   #3
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- clean fuel injectors (stated above)
- clean throttle body
- put a can of Seafoam in the intake and gas (can also help with the above two suggestions)

The Seafoam treatment did wonders for our '97 that had a very rough idle that would also cause a misfire on occasion.
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Unread 08-04-2011, 05:31 AM   #4
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Start with fresh Champion copper plugs gapped to .035, new plug wires, distributor cap and rotor.

Failing to freshen tuneup hardware when symptomatic often results in the chasing of your tail.
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Unread 08-04-2011, 02:49 PM   #5
rustyabiding
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Ok Ill try all those suggestions, When I looked at all the plugs, wires, cap and rotor they didnt seem that bad but looks can be deceiving I guess haha. Ill update when im finished, Thanks!
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Unread 11-12-2011, 12:25 PM   #6
rustyabiding
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I put in new plugs, wires, cap, rotor, and seafoamed it. It didnt make one bit of difference. Still does its chug chug chug chug chug chug chug constantly. How do you test the injectors? Or could it be something more serious?
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Unread 11-12-2011, 11:18 PM   #7
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You can tests the injectors by swapping them (swap #1 and #3 injectors, put them elsewhere). If the codes follow the banks where you put the injectors, then you know.
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Unread 11-13-2011, 04:14 PM   #8
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Ok That makes sense, Ill try that Thanks!
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Unread 11-13-2011, 04:56 PM   #9
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could be the map sensor
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Unread 11-13-2011, 10:58 PM   #10
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Quote:
Originally Posted by Absolutexero View Post
could be the map sensor
I was actually thinking that (MAP or vac leak). Probably the next thing to check after the injectors.
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Unread 11-14-2011, 06:06 AM   #11
AmbuGrl
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Check the wires from your upper O2 sensor to make sure they arent damaged.
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Unread 11-14-2011, 12:23 PM   #12
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Reset the computer by disconnecting the battery. Leave it disconnected for a few minutes then reconnect.
If the timing in the computer is off, it will reset and relearn the timing. This may or may not be the problem, but it's the simplest thing to do before you go throwing money at it and spending hours troubleshooting.
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Unread 03-26-2012, 10:53 AM   #13
rustyabiding
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Sorry It took so long to get back, I got hurt and have been laid up for months but I replaced all the injectors and still no change. I think it could be something with the head or the timing chain????
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