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Discussion Starter · #1 ·
Hi everybody

I just hopped in to my YJ this morning. I started the engine and the YJ would turn and idle around 1000RPM. After a few seconds, it would drop to around 700-500RPM and fluctuate. After a few seconds of that, it dies.

What could be the issue? It's the 4.2L I6
 

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Discussion Starter · #2 ·
Another thing, before it would idle high, and after a few minutes of sitting/warming up, it would to drop to 1000RPM
 

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I would check the Idle Air Control valve. It is what lets the air bypass the throttle body when your foot is off the gas, and the TB is closed.

Bad Throttle Position sensors can cause similar issues, since they can fail more than one way. I would start with the IAC if it was driving fine before that. Usually if the TPS goes, it will do things like buck when you give it gas and act weird under power.

If your Jeep wont start just turning the key, but starts when you step on the gas and turn the key, I would do IAC.

Also, if your idle was at 1000RPMs, I would check your intake manifold bolts. They are known to turn themselves loose over time letting a little air in raising your idle 100-300RPM usually. In my experience, the one towards your firewall usually are the loosest.
 

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Discussion Starter · #5 ·
I would check the Idle Air Control valve. It is what lets the air bypass the throttle body when your foot is off the gas, and the TB is closed. Bad Throttle Position sensors can cause similar issues, since they can fail more than one way. I would start with the IAC if it was driving fine before that. Usually if the TPS goes, it will do things like buck when you give it gas and act weird under power. If your Jeep wont start just turning the key, but starts when you step on the gas and turn the key, I would do IAC. Also, if your idle was at 1000RPMs, I would check your intake manifold bolts. They are known to turn themselves loose over time letting a little air in raising your idle 100-300RPM usually. In my experience, the one towards your firewall usually are the loosest.
Thanks, I'll check that out
 
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