Backfire through the intake,won't idle

jrt2nd

jrt2nd

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So, we took my wife's 97 tj to get groceries yesterday. When I started it after shopping it ran rough and backfired through the intake a couple of times, but then it straightened out and ran fine back home. Then this morning it started but wouldn't idle. She could keep it running by keeping it revved up but as soon as she let off the gas to put it in gear it would die. I read a bunch of post on similar backfire problems but not quite the same. I feel like I should know how to go about trouble shooting this, since I've maintained all my vehicles all my life and even taught high school auto shop 40 years ago, but I'm at a bit of a loss where to start. Maybe I'm getting too old and losing my memory:rolleyes: I don't want to just start throwing parts at it. My guess is that it's something to do with the timing; maybe a sensor or it needs a new cap & rotor? Anybody have experience with this type of problem or can point me to a link that could help?
 
Well can't say I have ever had those symptoms and I know you don't want to just throw parts at it. But for the price of a new cap, rotor, and plugs it's worth a shot to see if it's that simple and a bad distributor cap can definitely make it run rough.

I have the 98 Inline 6. and I have replaced those parts. The only other thing I have had go bad is the pickup coil. I replaced the crank shaft sensor at that same time also. 125K miles now. I have had a Rotor just fall apart. but, when that happens the Jeep just dies quickly.

Different animal 2 cycle etc. but, my Sea doo will do exactly what you are describing if my plugs foul out. new plugs and it's back to normal.
 
jrt2nd said:
So, we took my wife's 97 tj to get groceries yesterday. When I started it after shopping it ran rough and backfired through the intake a couple of times, but then it straightened out and ran fine back home. Then this morning it started but wouldn't idle. She could keep it running by keeping it revved up but as soon as she let off the gas to put it in gear it would die. I read a bunch of post on similar backfire problems but not quite the same. I feel like I should know how to go about trouble shooting this, since I've maintained all my vehicles all my life and even taught high school auto shop 40 years ago, but I'm at a bit of a loss where to start. Maybe I'm getting too old and losing my memory:rolleyes: I don't want to just start throwing parts at it. My guess is that it's something to do with the timing; maybe a sensor or it needs a new cap & rotor? Anybody have experience with this type of problem or can point me to a link that could help?
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Inconsistency leads me to think it’s a sensor. I’ve had a crank shaft positioning sensor go bad and it would give me random times of misfire or a bad back fire. Make sure your idle air control module is clean too. Hope that might help or narrow things down some.
 
Backfire through the intake is usually lean mixture. Vacuum leak, low fuel pressure something like that.
 
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So, I'm not sure what the problem was. I replaced cap and rotor and then it would idle, but not well, and when it warmed up it ran ok. So I cleaned the idle air solenoid, but it still had rough idle issues until it warmed up. Then, after a few days and a new tank of gas, it cleared up and ran and continues to run fine. Possibly some bad fuel? Who knows? Anyway,thanks for the replies.
 
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