Rough idle on 06 4.0

[johnathan25]

I've been having a really rough idle on my 06 mustang with the 4.0. In park it doesn't idle nearly as bad, but it's still rough. When put in drive or reverse, the rpms drop so low that it nearly stalls out. On average it idles at around 550rpm at operating temp, however when put into drive or reverse it'll drop down to 400 or lower, as well as at a stop light it'll intermittently drop down to 400 or lower. While driving up the road it drives nearly perfect with no issues. I'm getting a p0171 and p0174, however I cannot find the cause. There are no vacuum leaks, no exhaust leaks, intake manifold gaskets have been replaced, maf has been cleaned, throttle body has been cleaned, fuel filter has been replaced, and both o2 sensors have been replaced. Ive also reset pcm and did throttle and idle relearn after doing all of this but to no avail. I'm stumped as to why I'm having this idle problem. Any insight would be appreciated!

 

[86GT351]

Do you have a scanner that gives you data?

 

[johnathan25]

Do you have a scanner that gives you data?

Yes I do! What should I be looking for?

 

[TexasBlownV8]

What is your air intake setup? Using a CAI without a tune? Other mods?
Normally, your issue would be caused by the spark plugs, but they don't throw lean codes on both sides at the same time.
Or the fuel filter may need changing.
But as mentioned, use a scanner and monitor the front O2 signals/voltages, and fuel pressure, and maf voltage. It'll show if running rich at idle.

 

[86GT351]

Yes I do! What should I be looking for?

Fuel trims. Take a picture of your fuel trims to see where they are.

 

[RobErnst]

Any update?

 

[wildlifeguy]

This forum is tough. I'm used to the jeep forums that have 5 replies before you can refresh the page. I'm still learning, so would like to see an update as well. As asked above, I would like to see the fuel trims and more information about setup. Mine had a code for EGR insufficient flow. It was also having some funky idle issues where it would surge 2-300 rpms often when stopping and would settle at a low rpm. It did this about 7 out of10 times after coming to a stop. I didn't think the EGR would affect idle so I kept chasing vacuum issues. I bit the bullet and replaced the EGR last weekend which fixed the code and I haven't noticed the idle issue since.