Idle won't stay put

[TheGr8Schlotzky]

When i'm idling for a longer period of time, i've noticed my tach won't stay in one place. The rpms will move between 700-1100 mostly randomly up and down, sometimes down to 600, when the lights dim for a sec and it revs up to about 11-1200. i've also noticed a probably unrelated sound, sounds like a broken hanger i guess around the cat, or something is rattling in the cat..only happens from about 700-1000 though, no rattling at any other RPM.

The car runs perfectly fine in every other aspect, no jumping or roughness driving around, and it's not necessarily rough at idle either, it just won't stay in one place.

forgive my n00bness, i have very few chances to learn from experiance and searching hasn't showed me what i'm looking for.

I know the plugs and wires are within 15K old.
-no ses

[TheGr8Schlotzky]

Re: Idle won't stay put

I guess i never really noticed, but it doesn't happen all the time. I drove my car this morning and i idled a while to check it out and it was right at 750ish and didn't fluctuate. So it happens sometimes, maybe when the car is cooler, thought my temp gauge never goes above 1/4..i don't think i've ever seen it even get to 1/4 infact.

[slow6]

Re: Idle won't stay put

your temp gauge doesnt go over a quarter of the way?

If your engine is not getting up to proper operating temp ( 170 - 200 ) it is bad

Sounds like your car's computer is making it idle that way which is normal for it to compensate based on the conditions reported to the computer

[TheGr8Schlotzky]

Re: Idle won't stay put

according to my temp gauge, the temp is slightly under 1/4 after driving a while. I don't remember in the summer, but i think in the warmer weather it got to slightly above 1/4. Never gets close to the halfway mark though so idk what's up..stock thermo and all. Just a CAI.

I know the computer would adjust the idle accordingly, but it seemed a little bit spazy, over the course of say 5 seconds it would go up 100, down 200, up 100, up 200, down 300.

[slow6]

Re: Idle won't stay put

Maybe stuck open thermo? Maybe your fans are coming on? IDK

[TheGr8Schlotzky]

Re: Idle won't stay put

Here is where I'm at after about 15 minutes of normal in town driving (about 55* out):

[nascar24jd]

Re: Idle won't stay put

That does not look too bad, probably between 170 and 180.