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Old 11-28-2012, 10:13 AM   #1
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Bouncy idle

2000 tj sport 4.0 automatic 41,000 miles. In park Or drive at idle with brake applied idle bounces up and down. Nothing drastic the rpm needle moves slightly up and down. It also seems to idle very fast. I can release the brake and it actually will go 10 mph. Is this normal. This is on flat ground of coarse.

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Old 11-28-2012, 11:02 AM   #2
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Quote:
Originally Posted by WVU Mountainman View Post
2000 tj sport 4.0 automatic 41,000 miles. In park Or drive at idle with brake applied idle bounces up and down. Nothing drastic the rpm needle moves slightly up and down. It also seems to idle very fast. I can release the brake and it actually will go 10 mph. Is this normal. This is on flat ground of coarse.
Do you get a check engine light? Vacuum leak or bad Throttle Position Sensor (TPS) would be my guess. Perhaps others will have better ideas.

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Old 11-28-2012, 02:17 PM   #3
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Nope. No CEL.
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Old 11-28-2012, 07:32 PM   #4
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clean or replace your Idle Air Control valve .
this would be the first thing i would do.
a very slight like just the width of the needle movement is could be caused by old worn vacuum lines that look ok but the rubber is not pliable enough to have a good seal on the fitting ( i like replacing all my vacuum lines every 5 years )
it can also be that your electrical current not flowing thru the wire harness as easy as when it was new and if your battery older and weak or alternator is weak it can cause pulsing singnals in the current and cause the bounce.
you see it happen when folks add high output amps to the stereo but don't upgrade the charging system.
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Old 11-29-2012, 03:16 PM   #5
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How hard is it to replace the vacuum lines?
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