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Old 10-09-2013, 09:25 AM   #1
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Codes 51, 21, weird smell and low rpms in neutral?

I start the car up and its fine but after a couple ofinutes my rpms drop below 300 in neutral, I get a funny smell sometimes too.
Code 21 and 51 are both O2 sensor related if I believe, but the thing is I have already changed my only upstream one.the catalytic converter was changed about 4 months ago. I'm cleaning the throttle body saturday. I have a feeling it might be the exhaust as it has a rattles some. Any ideas as what it could it be?
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Old 10-09-2013, 09:30 AM   #2
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What model year & engine?

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Old 10-09-2013, 09:31 AM   #3
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What brand sensors were used when replacing? Anything other than NTK and they will likely still cause problems
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Old 10-09-2013, 11:08 AM   #4
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Its a 1997 2.5 wrangler se and I used a bosh o2 sensor
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Old 10-09-2013, 11:35 AM   #5
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I just started her up and got some really high rpms, 1800 tto 2000 range and I got that smell then really low rpms in neutral...
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Old 10-09-2013, 01:44 PM   #6
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Quote:
Originally Posted by WranglerRebel View Post
Its a 1997 2.5 wrangler se and I used a bosh o2 sensor

The idle issue is likely either a vacuum leak or a throttle position sensor (TPS) or Idle air control valve (IAC). The IAC can be taken out and cleaned so that would be my very first step, followed by changing those bosch sensors out for NTK sensors.
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Old 10-09-2013, 05:26 PM   #7
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Quote:
Originally Posted by Big Sarge View Post
The idle issue is likely either a vacuum leak or a throttle position sensor (TPS) or Idle air control valve (IAC). The IAC can be taken out and cleaned so that would be my very first step, followed by changing those bosch sensors out for NTK sensors.
X2 on all that, especially since Bosch 02 sensors have a reputation for causing problems on Jeeps.

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