I don't know where to start here, sometimes (more often than not now) when I first start my car it won't hold an idle. After I drive 10 min or so it will hold an idle but very low, like around 300-400 rpm. After driving a little more it will return to normal. Any ideas where to start? It's a 96 4.0 manual trans 4x4. Thanks

 

Could be idle air controller.... the intake air temp sensor might too but idk.

 

Here's some new info I noticed: usually my check engine light is perpetually on because I've been running with out a cat in my exhaust. I noticed that when my car won't hold an idle the check engine light isn't on. When the check engine light comes back on then my car runs fine.

 

Have you ever changed your O2 sensors?

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Nope. Where are they? How can I test them?

 

They are on the exhaust pipe. One is on the down pipe just past the manifold and the other is behind where your cat would be. Testing with a multimeter would be easiest. They are like $15 at autozone. Have you taken it anywhere hand had the codes checked?

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