Rough Idle on 2000 4.0

[Jake21]

Occasionally my engine idles a bit slow and rough. Running it over 3000 rpm makes it go away for a period of time lasting anywhere from a few days to weeks. I did change the Coil Pack last year and although it seems to run smoother, the periodic rough idle remains. Any ideas?

Thanks Mucho
JJ

 

[Chris]

Have you tried cleaning your IAC and throttle body?

 

[Jake21]

Have you tried cleaning your IAC and throttle body?

Have not.

 

[Chris]

Have not.

That's the first place I'd start as it's almost free and very easy.

See here: How to clean your IAC (Idle Air Controller) valve

 

[CreepinDeth]

If this is happening, it should have thrown a code
It happened to me in Tennessee on my way home with it

I cleaned my IAC and throttle body but the issue is still there
Im gonna replace the IAC next

 

[Jake21]

That's the first place I'd start as it's almost free and very easy.

See here: How to clean your IAC (Idle Air Controller) valve

Cool. I will give it a shot. Thanks

 

[WestCoastDan]

Bad O2 sensors will also cause a terrible idle, but that usually comes w/ a code or 2.

 

[Jake21]

Bad O2 sensors will also cause a terrible idle, but that usually comes w/ a code or 2.

no codes. and why would running the engine over 3000rpm have an effect?

 

[WestCoastDan]

I didn't mention high RPM, just idle.

 

[Jake21]

I didn't mention high RPM, just idle.

I know. i did. the rough idle goes away for days and even weeks after running at 3000rpm for a short period. even 30 seconds

 

[CreepinDeth]

Yeah mine clears after I rev it the same way
Within seconds its fine

One out of every 5 times it will come back briefly at idle while still cold

 

[WestCoastDan]

That I s exactly how my ‘03 4.0 acted before it threw the O2 codes.
I replaced the affected sensor myself and it cleared the code and solved the rough idle.
Maybe a stupid question, but did you logically assume there are no codes because there is no CEL light on, or did you actually check for codes and there are none listed?
Imagine your CEL lamp having burned out or come disconnected and there really is a code… that would be my type of luck.

 

[Jake21]

Sorry for the late reply. there was no code before, but today I got a misfire in cyl #3.

 

[WestCoastDan]

Did you pull the plug and check the condition? It could be as easy as needing new plugs.

 

[astjp2]

Just install new app985 plugs.